Sins of a Solar Empire was boring as hell if you ask me, no variation between factions, no story/campaign.
I didn't feel these were particularly hate-worthy points, but yes they could be considered weaknesses. The different playstyles of the factions open up only after some time of playing, but then you'll encounter the general shallowness and lack of balance (at least until versions 1.03-1.04, when I stopped playing.) The lack of campaign is a non-issue to me (how many RTS games have campaigns actually worth playing?), but it's quite understandably a weakness of Sins.

Quote Originally Posted by Zenicetus
The UI seemed weird and unintuitive
This is somewhat baffling, though - the UI is generally considered one of the strong points of Sins. Could you elaborate a bit?

Quote Originally Posted by Martok
I would argue that the Space Empire games have too much stuff -- I always feel overwhelmed by the enormous number of ships, buildings, and technologies at my disposal.
Yes, Space Empire series is a bit too complex for its own good. It does try to alleviate the complexity with a lot of automation options, but doesn't do it very elegantly.

Maybe it's time to give Sword of the Stars another whirl. The lack of peaceful options never bothered me - gotta bomb 'em fugly tentacle dudes to oblivion anyways - but the shoddy combat interface and unsuitability for multiplayer did.