Its got great graphics for such a cheap game. The gameplay is fun. It can be laggy at times, but really I only lag when I do a taint run and 100 or so zombies spawn all at once.
Singleplayer: You go about doing quests, basically shaping the world with what you do. My friend recently completed it two ways; good and evil.
Multiplayer: There are 3 main servers, 2 European and 1 American, and several servers inside each one. Inside each of those, the player can choose to make an RPG character or a PVP character. On the American server, I have never seen a PVP server with any people in it. Lots of complaints from my friends are about the PVP, but there is a solution. In the RPG, players can choose to do arena mode, where there is team deathmatch and team monsterhunt etc. The RPG server isn't always packed, I think that the most I've seen was 30, and that was on a weekend. But, the admins and mods are on a lot, so I've never seen a cheater. Everybody in the small community is nice, and your guild member will often start you out. One of my guild members says he is making me a kick-ass axe.
Tis fun.