I play both eve and sins, albeit more of the former. But both are great games.
Eve Online - Massively Multiplayer Online (MMO).
More of a social game. You have to co-operate with others to a lesser degree, depending on what you want to do. But if you are into player vs. player (PvP), cooperation is a must as you are a solo pilot. The ship you fly are usually specialised. Think fantasy like WoW in space. Means you need a party of damage dealers, healers, melee and etc.
But Eve is brutal as you say. Trust the wrong ppl and you'll lose quite a bit of fortune. Sabotage, piracy and theft are somewhat condone and allowed. But all in all, I love it and in my opinion, one of the best MMOs I've played so far.
As it's an MMO, you must be connected on the internet at all times to play as other ships you see are real life players.
Eve is more like Role Playing Game (RPG) but in space.
Sins of A Solar Empire - Single Player with Multiplayer Capability.
The only thing that is the same as eve is that Sins is a space based game. That's all.
Sins is a strategy game, a hybrid between Real Time Strategy (RTS) and classic Turn Based Strategy. Like what Annatar says, you are the overlord of your empire. You build your army, and then strategise to crush your opponent.
Sins' learning curve is not as steep as Eve's, but it will take awhile nevertheless to get the hang of it. You'll learn how to build your armies, using different combination of ships, as well as choosing which technology path to go for (yes you need to research certain technologies to be able to unlock more potential abilities and ships)
Sins is a single player game, meaning you can play alone against your CPU opponents, or hook into the server and go multiplayer and fight other humans.
In Sins, you strategise to win, such as when to build your army, ally with who, how to repel forces twice your size (if possible) attacking your planets and all that. The pace is rather slow so it allows you to think and formulate a plan (just don't panic).
All I can say about Sins is if you haven't try it, do so and you'll find out for yourself it's a great game.