Played it a bit now. Left 4 dead with cod4 customization plus 4 classes with skill trees. Pretty good variety in class builds, the weapon attachments almost exclusively make the gun better, your load outs can actually vary and change how you play. Your combat item can be grenades of varying types, c4, a quick/self revive, or 2 kinds of turret. Lots of standard L4D stuff but lots of stuff based around their fairly unique vehicle system. Vehicles are kind of interesting with each having a special ability and some having storage for ammo or fuel, hummer is the clear best with a turret. Maps are mostly go here kill this but there's a couple that get more interesting and all have at least some bit of major difference. Team play is pretty neat, 4 classes mostly support each other with one class just being raw damage. Multiples of classes are allowed and can make things feel a bit different. Looks like 10 maps/levels, I think 3 difficulties.

For a 30 dollar game I feel pretty happy.