Valor: A modern day army with modern equipment you would find now (M4A1, SCAR, M14EBR). Gun attributes are moderate fire rate, moderate accuracy, and moderate damage. Modeled after the US.
Raven: A technologically advanced army with expensive equipment (AUG,F2000,G3). Gun attributes are low accuracy and low damage, but high handling (low recoil) and rate of fire. Modeled after Europe.
SVER: An economically deprived guerilla army with cheap russian equipment (AK74U, AN94notcheaplolz, Dragunov). Gun attributes are low rate of fire, low accuracy, low handling (high recoil), but high damage per bullet. Modeled after Russia/China.
If you can handle the intensity of 64, 128, or 256 player games, then you will have a blast in this underrated yet incredibly fun game. If you can't, then you will hate it for your lack of skill and common sense and go back to playing easier games such as Black Ops or Bad Company 2.
Joe: "MAG? Massive Action Game? That game with 256 players?"
Bob: "Yeah, it's fun."
Joe: "Pfft, yeah; if you're on S.V.E.R."