I know I have walked this road before. Infinity is the main tabletop competitor to 40k for my Hobby Dollar (along with Dust Tactics, though I suppose that is a boardgame). One of the things I like so much about it is that the rules are free online.
Oh, and the models are awesome.
Oh, and it seems to lend itself to using my Halo Actionclix figures for counts as.
Now all I need to do is actually learn how to play this game.