Alright, half life 2 is a great game. everybody who buys it LOVES it, its a classic but you will be amazed by the gfx. also, red faction guerilla is so much fun, I'm so mad at myself for losing it when my OS crashed. The gameplay is great and the destructable enviroment just adds to the fun. Hope i helped your decision.
Newegg has Unreal Anthology for $10. It consist of: Unreal, Unreal Tournament, Unreal II and Unreal Tournament 2004. As of a few days ago, Newegg also had Unreal Tournament III for $10. Both items include shipping.
vor strategy: try supreme commander (forged alliances or not)
its a lot different of the usual strategy, huge maps (really, if you havent seen this game, you haven't seen this size), a max of 1000 units/buildings, the game is designed to do huge battles.
you can send experimentals(expensive but very strong units) to wipe out an entire base, or just to get it destroyed without destroying anything.