I think these are the major gamer types:
1) casual gamer - plays easy accessible games, or only plays occasionally.
2) regular gamer - plays harder more complex games. usually plays more than the casual gamer though gaming is still entertainment rather than a hobby.
3) competitive gamer - tends to play online RTS, FPS or MMORPGS, spends large amounts of time improving their competitive edge, tries to be the best. May play one game obsessivly.
4) hardcore gamer - loves games, to the hardcore gamer gaming is a hobby, they are involved in many facets and aspects of gaming culture, probably spends more time gaming than the regular gamer though won't fixate on one game like a competitive gamer.