I loved Endless Space! Not sure if I'll pick up the expansion yet, even though I kind of feel obliged to after all the free content they've released for the game thus far.
Re Space 4X games: If any of you guys are thinking about Star Drive, eeeeehhhh. Proceed with caution. One of its signature 'features' is actually a hellish chore.
I'll pick up the expansion if it's on any kind of sale during the steam summer sale. I hope it gets like 25%, although it wouldn't surprise me if not. It's definitely a lot of fun though, can't recommend it enough for anyone who likes TBS games.
Also not sure Civ5 is the best game to try Big Picture mode on... I feel like big picture is best for games that benefit from sheer "size/impression", like Action games & RPG's. Less so for strategy games, where graphic prowess isn't the most important factor.