Played EVE Online for about six months several years ago. In EVE you are piloting a single ship at a time, although you may own a whole fleet of ships. EVE has a wide variety of ships for different purposes from warships of all kinds to mining boats and freighters.
In Sins you are controlling fleets. So game play seems very different to me. In EVE, you are talking six months to a year to really get rolling in your specialty whatever it might be. With Sins, games last a few hours usually. What you gain each time you play Sins is personal skill. In EVE you can now queue a series of skills to keep leveling up even when you are offline. It can take two weeks or more of real world time to learn just the final level to get to max in many of the skills. But the skill leveling rolls on even when you are offline.
Both games convey a feeling of being in space. I think EVE might win the graphics battle by now, just looking at videos. But Sins won't hurt your eyes. The graphics in Sins is simply excellent and there are mods to make it even better.
EVE was fun and challenging, the open PvP is something you either like or you don't. Beware! You can hide in the layers of space patrolled by the police ships, but going down towards zero space is where the gut gripping excitement and real loot is. And down there, getting ganked is a way of life for a lone player. So a good corporation is a must! I was in an excellent corporation. Just playing with those guys was a riot and a hoot! Every single night!
How I got in, was just out in my mining boat harvesting a bit of ore. When this cruiser sailed up and blew up my nearly defenseless mining boat. For some reason he did not kill my escape pod. So, I told him you just wait right there and I'll be back. My best frigate was in that system, no real match for a cruiser but I would dent him good! So I came roaring back out and had dented him much less than I had hoped when he asked for a cease fire. He had thought I was a farmer, a bad thing to be, and apologized for blowing up my mining boat. He told me he would send a huge amount of ISK to me by way of compensation. And we chatted and one thing led to another and because he thought I was insanely aggressive he said I might fit in well with the other members of their corporation. Which I did. That's been years ago and I could still fill pages with anecdotes and stories of all that happened.
Rule One of EVE is "Never fly anything you are afraid to lose." Because it will get blown out from under you, sooner or later. EVE has the most fierce, competitive, vicious, unprincipled, cruel, lying, cheating, scamming, downright evil ... and also the friendliest and most helpful community of players of any online game out there. Want to be a "law abiding" member of a corporation? Sure. Want to be an out and out Pirate? Yawrrrr! Want to be a miner? Sure. Want to be a manufacturer? That works. And there are four factions and ... it just goes on and on.
You do get a good tutorial in EVE, and for a couple weeks you just run quests in high space with no real threat from other players. They give you plenty of time to learn the game in relative safety and there is a lot of game to learn. The universe of EVE is huge, really really big. And the complexity and depth of everything just keeps on coming. But you learn it all one bit at a time. I never felt overwhelmed or snowed under.
There is a Sins of a Solar Empire demo over at bigdownloads.com. I think the demo still works?
And, EVE Online has a 14 day free trial so you can see what you think of it before plunking down money.