I had a similar dilemma recently. I would say the most intriguing games on the market right now are:
Dragon Age (Don’t have)
Mount and Blade Warband (Don’t have Warband, just vanilla)
King’s Bounty (Don’t have, but everyone swears by it)
Civilization 5 (Have and love)
The Guild 2 (Just bought… looks okay so far)
Starcraft 2 (Don’t have)
Star Ruler (Don’t have)
Elemental: War of magic (Have, you should really avoid this one)
Ehh, those are the games I have been thinking about purchasing. I went with The Guild, not exactly sure why. I think part of the decision was that my wife has been reading the book “Sons”, the second in “The Good Earth” trilogy, and a lot of the events in the book sound like they came from a “The Guild” LP.
Personally, I would say avoid Mass Effect. I thought the game was pretty bad. Combat in that game is really clunky. It is hard to get yourself killing the right people before the target and shoot you at AI speeds, even with pause. I am pretty sure I am in the minority on my assessment, but I only played that game for a few hours before uninstalling.
Really though, I’d suggest getting some old games, if you haven’t played them. Age of Wonders is on Steam and Impulse and it is a great old time Strat game. I like all of the versions differently, but equally.
Impulse also has Master of Orion 2, one of my all time favorites. Good Old Gamers has Fallout 1 and 2, which are both a hell of a lot of fun, even if they are a bit dated.