If you do not know what Urban Dead is, its a zombie survival game where you can play either a zombie or humans, and fight it out, this game is similar but add in vampires, and a whole load of new elements.
Essentially, its gameplay is similar to UD but most of the content is very different to it, of course there are some similar items, plus there are vampires and zombies
Things it has that UD does not have that hellrising has ( Not gonna list everything, just some stuff)
One thing you all might like though it it has much faster ap, 5 ap per 5 minutes actually.
It has a bigger roster of weapons in both melee and in guns and projectiles, such as the aussualt rifle found in forts ^^
Obviously a whole new skill class with vampires added into the game. Plus both humans and zombies have a wide variety of skills.
Many different buildings in the game, also two alternate maps, one being a country town, and the other a slow AP town for people who prefer a slower paced game.
http://www.hellrising.com/index.php
http://wiki.hellrising.com/index.php/Main_Page
Wiki link for game info
