There are 3 Game modes: Battle Mode(standard PvP fare, only mode that lets you gain License Points, which are needed for getting better guns), Mission Mode(PvE, where do you missions for EXP) and Co-Op Mode(You fight zombies. Some missions include defend the base, defend your female commanding officer and a mission which can be described as 2D Left 4 Dead).
Game has 4 characters: Carl(who's the balanced guy), Burton(big guy who's good at the frontline due to high health), Marie(cutey who's good at long range) and Ai(hot babe who's good at scouting and support).
There are 5 weapons you can carry: Pistol(mediocre firing rate, but has infinite clips), Rifle(rapid fire, pretty basic stuff), Sniper Rifle(long range, only gun that lets you headshot), Rocket Launcher(slow as hell, but pretty much insta-kill to any normal person) and Shotgun(deadly at close range).
Other problems exist though(for example, I instantly disconnect from a game when I enter a PvP room with more than 10 people) but those aside, it's a surprisingly fun game. Fast-paced 2D shooter madness. It feels like Metal Slug. Though PvP is encouraged, PvE isn't a slouch, though it only gets difficult in the later stages, where you fight a tank for a boss. There's also an option that lets you turn on Blood and Gore, meaning people bleed when they get shot, people explode into gibs when directly hit with explosives and headshots from a Sniper Rifle can blow their heads off.
Oh right. My IGN is Stadtfeld, character is Marie.