Hah! Not had quite so much fun since I discovered Command and Conquer.
Doorkickers is a fun strategy game that I'm actually really quite enjoying. I think it's the tactics thing. It's well worth the free alpha version download (full game is $8, although you can pay more for more perks) just to see if you like it and it won't break your download bandwidth at 140Mb. Doorkickers Site (http://inthekillhouse.com/doorkickers/)
If you want to see what it's about, then have a look at TotalBiscuit's review here. (http://www.youtube.com/watch?v=V8me_88G0eU) He's another discovery and his videos are well worth a watch.
-H