To truly be a gamer, you should be judged on how many games you play, how long you play your games for, Is it number one on your what to do on a weekend list, what sorta games you play, when did you start, etc. A gamer should play a variety of games, so in my eyes i see no gamer if it is somebody who ONLY plays MODERN WARFARE 2!
I consider myself a gamer. I like sandbox games like just cause 2, mercenaries 2, prototype, incredible hulk: ultimate destruction. Please note prototype is nothing but a copy of IH:UD. Same maker, same physics, same styled moves but only add in zombies and you can drive and disguise!!!
I think people who play games that take ages ( RTS"S, MMO'S ) They are dedicated to games. if you play mw2, halo 3 and similar shooters often enough ill call you a gamer, otherwise you other people can go die. You know, those people that only play one game and start calling themselves a gamer!
Also all people any people who play on the computer, they are gamers!!!!! except for the ones who play Peggle. or barbie. lol.