A Nice Game.
Pro's: Fun Action that is easy to get into, as well as the ability to run on walls, flip off of walls, learn different styles, wield guns, swords, daggers, etc... Map variety, many maps, and modes to play on.
Con's: Hackers, of course, like almost all online game, there WILL be hackers.., glitches in some maps, mostly unfriendly community, with almost whatever you do being a problem to someone. Example: If you get a weapon such as a machine gun, you will almost for sure be kicked for being a "sprayer noob", or if you flip someone with a sword on a map with holes that you can die from falling into, you will be a "flipper noob". The community is VERY unfriendly, with an almost lack of GM's, only 2 or so, so a need of GM's as well as administrators in-games. Also, it is easy to get bored if you have played for more than a month, the replay value isn't too strong...
GunZ: The Duel, overall, I recommend at least trying it out, because at 210 Megabytes, it shouldn't take up too much space, and almost any computer that has XP or Vista should be able to run it smoothly.