I've been putting some time into Battlefield Play4Free. It's actually a pretty cool game, being that it's free (about 90% free because of guns). There are some weapons you can't buy unless you use some real money, but that's not too expensive. It will take a long time for me to save up for my M60 LMG using the game's credits, but I can get there. (You unlock a gun by either saving your game credits, or using real money.) You'll have to get used to the feel of the game, but it doesn't take long.
I've been playing it on its highest settings with no trouble.