I love turn based strategy, but I can't really get into greed corp. The gameplay mechanics just rub me the wrong way I guess.
I personally didn't find magic 2012 to be that bad, though mainly because I stopped playing magic a long time ago and appreciated seeing how the game has changed a little bit. Very much a causal game given the lack of all but token deck editing, but I suppose I am mostly a casual magic player these days :p
I could mention risk: factions, but I haven't played it, just seen some vids. Has a short campaign mode, and not a whole lot else to offer...
Frozen Synapse is another I haven't played but have seen some vids and it very much is on my to buy list as it has a lot of awesome things going for it. You have a group of people you give commands to and can simulate what the opponent might do and see how it plays out before you commit to a move. Very VERY tactical.
Not all too much offered on steam for these types of games sadly. About the only other thing I can think of is Gratuitous Space Battles, which isn't really a board/card based game, but there are some tactics involved, the game kinda relies on it because once you start a battle you can only watch it play out. I'd probably check out a video or two before deciding if it is you thing though.
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There is no shame in not knowing; the shame lies in not finding out