The only action game I ever played was CS and I still play it.
Now that I have mentioned CS
I suggest you all try Battlefield 2. I am currently playing a demo, but I think I'll buy the full version soon. It can not be described what it means to take part in a full scale attack, when a tank destroys the front and is followed by armored vehichles and infantry, not to mention the air support and parachuters dropping from the sky.
.....and that is not all, there are also the 32v32 teams, huge maps and the ability to run, swim, drive and fly on any vehichle one can imagine!