RTS
Conquest - very dated, but I still think it has a big edge on a lot of games since. If you've not played it you should. It was 2001? Remember all the RTS/4x games since and see where they went wrong by not doing stuff from it. It's a 2d RTS when every RTS was going 3d. Campagin has the funnest quotes in it. Characters were very good, a random unit response from an English character - Time for tea!
Haegamonia - legions of steel used simular concepts, but to be honest I don't think it really was any better - outside of graphics. Units were simplistic, not specialisation. Me bigger guns and hull me win! Multiplayer required an expansion, and it just didn't have polish. Some of the same team that made Imperium Galatica.
Nexus - was a ship to ship combat game that was made that I kinda rate as buggy as it was. You only have a couple of ships, but there was a feel to it like ships were slugging away at each other. I actually winced when getting shot at. Eve-online could learn from Nexus over 'feel'. If you want more 'epic' than SoaSE, this feels it, but it's a few ships - and online is pretty much dead now.
Homeworld - was utterly addicted to this game once. 2 to me, even though things changed - really it was a fancier interface imo. Just wish it had more. I actually feel the same way about Sins.
4x
Space Empires V is pretty epic, possibly too epic, I alway seem to restart rather than finish a game. Never got into it as much as Gal Civ. Definately one if you want to get lost in a game. Can get lost in the info overload and loose the game in your head.
Gal Civ I & II - what more can I say that hasn't been said - I rate it. Many a 4am finsih with that on 'skool' nights =/ For II get both expansions.
Imperium Galatica I & II, I like these, they have something about them. Sure they're real time, but there's a pause button, and that makes them have that turn based feel with statagy with them. Imp Gal II, I just love, there's something about it that I really really like. I've said it in jest before, but it's finding that odd girl who hides at the back of a room who isn't attractive absolutely georgous. It's the ground combat, it's the spying, it the dodgy fleet combat. I've modded that game a lot - and it's like an old friend. The first one is too scripted - but simular ideas.
MoO 1 and 2, Yeah, famous for being so good. If you haven't played them, you should do. Genre defining even now.
MoO 3, It isn't MoO, but patch it and spend a week or two learning it, and pretend it's not got MoO in the title, and there's some interesting ideas in there. Honest. You really do have to remember you're not playing MoO, your playing something completely different.
SotS - never got into it. Something has always pulled me away. I can't get my head tactically around the different racial interstellar moves. I'd like to say it's fate, but something there for me ain't right. Civ/TW:series/GalCiv I can't stop pressing that turn button. Just one more turn.... SotS I can. That's kinda a bad review in my mind - but it could be me.
SMAC - Alpha Centari - It's ground based and old but it's till fun, but I'll be recommending Civ before you know it, so I'll leave that there. I'd actually like to see the city populations more in Gal Civ.
Lost Empire: Immortals - never played it - but it's a year old and supposed to be the "biggest" out there. It's on my to do list. It has the label "souless", which worries me. When a game turns into a spreadsheet... euk. Talking of space game spreadsheets:
MMOG
Eve, Love it or hate it, right now it's the only really viable spaceship MMOG out there today. Yes, PvE sucks, it's PvP centric - even trade is PvP. It has an obscene death penalty, and it's very travel based. Takes an hour to fly from one side of the Galaxy in a fast ship - but 75% of that travel time you are a big red flashing target with the chance to die in sub 5 seconds. Get into a good corp/guild in 0.0, it can be the best game in the world. Sit in empire mining/mission running - it sucks long term. I personally find it far too much of a time sink. Need a new ship fast, and haven't prepared for it? Plan on spending an hour putting that together - and that can be in the middle of a fight. That's what kills it for me. I want to fly round in a spaceship and shoot stuff. I don't want to plan the logistics of having replacements at stategically important locations. My 36 million sp character is sat in 0.0, with 3 battleships in another region - I really just can't be bothered to fly over the 15 minutes there and then the 20 minutes back. Without the income that can generate, I can't afford to PvP with the guys, so meh, I ain't playing it.