I found this game much more enjoyable than I expected. You spend most of the game running/jumping around and killing Nazis by: a) Sucking their blood, b) Shooting them with their own weapons, c) Carving them to pieces with your blades, or preferably; d) All of the above. It's hard to explain exactly why the game is so great though, but I could hardly tear myself away during my first playthrough. Maybe it's the perfect combination of melee combat and gun action with authentic WWII weapons - maybe it's the awesome mood and setting of the game - or maybe there's just something about Nazis that make them so much fun to kill. Either way, this game is a winner.
You can kill enemies by shooting black holes at them. Seriously. What else do you need to know?!