Half Life 2

I haven't played many PC games lately, but Half Life 2 is perhaps the best action shooter I've played to date.

It strikes me as to why it's such a great game: it has an extreme amount of polish. Another developer's games that have this are Blizzard's. It shows because all the time you invest in the game is extremely fun because it's "fine tuned" to be that way.

Half Life 2 has it all for a great action game: lots of vehicles, great enemy AI, awesome graphics, great physics, the gravity gun, and more!