Twilight Imperium - Haven't actually played it but heard very good things about it from friends.
Played it some years back.
First thing to know about this game : it takes a whole day.
We would usually come at 10h00, quick lunch break, and finish around 19h00.
It's really a different sort of board game, not made for "casuals".
Other than that, it's a pretty decently balanced game (except of one overpowered race), of good board quality.
The map (galaxy) is made by the players, so always different.
There's a noticeable luck factor involved though :
-colonizing planets can give you free technology, or radiation, killing all your troops and interrupting the colonization process.
-All fights are with dice. And if you're unlucky, you'll see your superior fleet annihilated.
-Picking up "action" cards every turn, and some are remotely more powerful than others.
I personnaly quite liked it, since there's many means to claim victory.
But it's really long, so it's tough finding people ready to commit for that.