If you are talking from a "graphical" point of view, I will use the original Homeworld as an example. When the game was first released back in 1999 the graphics were awesome, because that was pretty much the best anyone could do with the hardware of the era. There was no comparison back then. HW was the best.

Back then most systems were running Pentium II's, and 1st gen AMD Athlons that basically broke the 1 ghz barrier the year before. 1 gig of ram, and a 256 megabyte video card was considered "high end", and Windows 98 was the the primary OS at the time.

Homeworld itself had limits. Meshes that were no larger than 700 triangles. With many under 200 tri's. A simple (and very non intrusive) UI. Homeworlds main drawback graphically was its hard coded memory limit for textures. Which was 32 MEGABYTES. There was No per pixel shading. No normal, or bump mapping. No shadows. Yet the game still looked beautiful, because the developers found ways to "work around" these drawbacks. Good game play was a big plus too.

By 2003 Hardware has advanced enough to where "Hey! We can create better 3d scenes!" With per pixel lighting, shadows, etc. etc. Homeworld 2 is a shining example of how the hardware of the time has advanced enough to add these new features. The differences graphically between Homeworld, and Homeworld 2 is like night , and day. Hence Homeworld became "dated", because that game does not have those features, and does not look as "pretty" as Homeworld 2. Unfortunately HW2's game play while itself is good. It is not as good as the original IMO.

The point is a game can be "timeless". I still play Total Annihilation, Homeworld, and Homeworld 2 to this day. Yet people "always want more". They always "want better". It is a "Keep up with the Jones's" mentality in the PC gaming world. An insatiable appetite. As hardware evolves so will software, and sooner, or later it will translate into PC gaming. Your game can be great, but no matter how good your game looks "There is always a bigger fish".

To answer the title of your post: Low polygons with poor textures and effects in a 3d environment.

Specifically for LH: Cities, Rivers, resources, basically everything is justified to the squares of the map.  This is definitely dated and it feels lazy.  Also the biomes should be more interesting and contrasting, each one should have its own effect on the game, and there should be more of them.

I'd like to echo what's been said already; it's the map/landscape items that need most love - a player spends most of their time in-game looking at the sweeping landscape.

Playing through my first game of FE:LH since I tried EWOM post-release 4 years ago; a striking thing is that the fine quality of the 2D art in backdrops (for 3D customised units, or leader picks) shows up the landscape assets that appear in the 3D environment itself.

Unlike some others on here, it seems, I really like Elemental's art style - but it would be great if the map trees looked like real gnarly, verdant or dank forest, for instance. And the sea like the kind of dark roiling expanse Elemental looks like it should have, with a craggy shoreline.

All that said, an obligatory repetition: None of it matters in the face of the gameplay - I still play MOM, teehee. And FELH is fantastic - I have no doubt I'll be playing it almost as long, woolly-looking trees or not.

I see the town graphics as superbly detailed - same goes for the unit graphics (unless you zoom in too close, but I'd still prefer to be able to) - I think for unit graphics Variety is more important than overall quality - it would be nice to have even more options available for unit appearance customization, especially at the mid-game chainmail-wearing stage.

1. fewer animation keyframes

the most difficult aspect of reality to emulate, and most processor intensive, is not the detail, but the movement.  we are constantly in motion, and subsequently so is everything in reality; in the most intricate ways.

2. attempts at detailed realism

any simulation of reality will quickly become outdated and overshadowed in the blink of an eye with the progression of technology, especially these days.  this is why animation, and #3, are so important...

3. the keys are stylization & art direction

the reason we're talking about video games and not board games with photographs is because the most fun parts of gaming are the interactive movements, not the emulated detail of static objects.  the underlying law of physical reality is that everything is in motion, nothing is actually standing still.  everything really is stylized by the movements of our minds & psychologies as we interact with it - a lucid dream if you will... like games.  video games really just boil down to psychological interactions as well.  static is boring, dynamic is captivating.  user experience is everything.  art direction just needs to clearly reflect the intended psychological experience, and it needs to be well animated.  look to all the greats of the 16 bit era, like nintendo, that are still beautiful today.  nintendo really gets it... practically everything they did for the snes, n64, gba, and gamecube still looks wonderful today, especially the zeldas (wind waker!) - because of the stylized art direction, and the movement!  hell, look at minecraft, or hero core, or heroes of might and magic 2, or all the great old pc adventures, for games that truly embody these principles.

I'm easy. If I can see the individual pixels that compose the objects in the game, I would consider a game dated.

I'd like to play a wildcard (if you will). Does Minecraft look dated?

As some people pointed out:

Number of polygons: If two games do the same thing, but one has more polygons (and assuming the artists are just as good), the other will have a dated look.

Art style: I personally loved the old 2D graphics. 2D games at 1999 managed to beat graphic-wise the 3D games of 2005 in terms of how good they look. Nowadays, the old 3D games look terrible, and 2D still just looks outdated.

Complexity of objects: If a battleship used to look toward the enemy, and suddenly a fiery hell will shoot out of it, we now expect to see the turrets move, target the enemy individually, and each one shoot.

Details: Using the battleship example again, when it being hit by the enemy fire- an old game will have the shots disappear, or have a general "battleship has been hit" effect. We now expect to see an explosion when the missile hit, and air flowing out from the breach, etc (or well, in a the near future).

In regards to FE, while it does not compete in art style with other games (it's quite unique, for good and bad), so we can't compare polygons, I'm not sure I can say that the art style look "current".

In terms of complexity, there's a dated look when people compare to other games such as total war (in tactical), or the world when compared to civ. Some of it comes from the whole customized units part, but it's easy to forget.

FE strongly fall on the Details part though. Just concerning the picture that came in the post: the water/beach looks like someone took a saw, cut a piece of land, and put it in some blue ooze. Inconsistent shadowing- looking at the units and the bare trees at the buttom, we expect that the general light's source comes from up and north. The city, forest and the treasure site do not have a shadow, though.

Beside that, the world looks as if it's built on squares. comparing the forest/plains border, it looks as if someone told the trees to stop.

The land generally keep being the same besides a few terraforms also bothers a bit. What, nobody ventures into the wild or works the fields? (as opposed to the upgraded terrain in civ)

While I didn't notice all of this, this is what came up to my mind when actually thinking about it. Part of it is choice, but part of it is what makes the game looks dated.

Judging by that picture only, since i never played the game, its not really the prettiest game, is it? Sorry to say that.

I wonder what is the reasoning behind using cell-shading tech...it makes the game to look sort of 2D-ish...surely if you wanted 2D game, you could achieve far better looking result with sprite based graphics.

So in my humble opinion, the issue is more with the overall stylization and art direction than with actual tech being used in this particular case.

Anyway, one thing i consider truly important myself for the game visuals, is the proper lighting. You can get away with weaker texturing and cheat with lower-poly models, but if the scene is poorly lit, no hiding that... thats why Homeworld 2 looked IMHO better than the first iteration of Sins from 2008, unlike Sins it had selfshadowing. In case of Legendary Heroes, is there any lightning at all, LOL? I see some weak shadows there, but overall it looks dull and unrealistic. Even stylized graphics can be helped with proper lightning, look at the Planetary Annihilation, while the models and textures are pretty basic, the sunlight and shadows make it look like battle of LEGO models, rather than computer graphics. I think THAT should be the target.

I realize its not easy to "simulate" the light to look almost life-like, for that i guess you need path-tracing anyway, but the closer you get to fake the results, always the better.

Elementals cell shaded look was never very impressive from the start.

Realism might look dated earlier but still looks great for most of the products lifespan,ala Shogun2 still looks great and all DLC is done.

Disciples 2 vs Disciples 3

Dated Graphic's mean little when compared to great game play.

Dated Graphic's are graphics that are well in the sega era of graphics. That's dated.

My opinion is that if the art is good, the graphic's will never matter. Sometimes you keep coming back because you love that art style. 

You wanna know what out does graphics at this point. Really good 3d. It's like movies, too though it your using black and white no one's gonna wanna watch it, it doesn't mean that it's not good. But no one is gonna watch it.

Like how far back do you go to watch a movie? And that's how know what's dated and whats not. I think i'll go back to when i was born, and a few years more sometimes. 

I wanna watch Nosferatu it's black and white. lol. I mean sometimes it's just the idea. Nosferatu draw's you in cause of the creepy looking vampire makes you wonder. Cause it was the artist side of it. 

Jaw's always pulls you back in cause it's Jaw's.

A game with really solid art direction can usually remain pretty timeless. Look at a game like Wind Waker or Mario Sunshine. Graphically they're not hugely impressive but because of their strong art direction, they still look amazing! Same reason why games like Borderlands will age so well or even Wildstar for that matter.

Games that go for 'realism' age faster because they're never perfect/realistic enough and the following year, new or optimized hardware will just put it in its place. For example, Oblivion looked great for its time, then Skyrim comes out and made it look like crap...

I think the problem is mostly that 'dated graphics' generally means that the game looks 'weird'.

Also with the release of many DX11 games this problem has become increasingly exacerbated. Every single DX11 only game has elicited cries of "this looks like garbage why does it need DX11" or "I can run BF4 at 100FPS why can't I run Tropico 4" or other such ignorant nonsense. IT's more or less that unless 'stuff is blowign up constantly' the game is 'not demanding'.

Or with UE4, where the lighting aspects of the engine are the really key elements, but yet games like Daylight come out and it's "this game blows why does it need DX11 or UE4".

I think this particular issue is going to be a repeated with Oxide games as similar comments were made with Star Swarm. "This demo looks like garbage, there's no specular lighting, etc" and had no concept of what the actual demo was trying to showcase. Again the 'I don't see the game blowing up star destroyers like it's the fourth of july so it must suck" attitude is increasingly prevalent with gamers that are 'supposedly' knowledgeable about video cards and engines (aka I read something on IGN 10 years ago and now I'm Carmack's twin)

Bit of a rant

As much as I like Civ 5's map graphics, they are soooo frickin slow to load.  When you see white instead of map texture until the game has a chance to load, that's a sure sign that the game is hugging the bleeding edge of technology instead of making a reasonable compromise between quality and what quality you can paint on screen before the user scrolls.

I mean, how hard would it be to load textures predictively based on the direction the user is scrolling?  I guess Firaxis are not bringing their A game any more.