Enough blood to drown a vampire!
I found this game very challenging in the early levels but once the exp started flowing it decreased in difficulty, especially after I was able to afford the laser cannon. Here's a hint to you guys, after you upgrade your pistols a few times, get a shotgun, then as soon as you can, get the laser cannon. You'll mow down everything in your path. But then I got curious about the other weapons and by far the most FUN weapon is the Pancor Jackhammer. I can just sit in front of my base and hold the mouse button down. Occasionally I'll have to dodge a zombie, but most of the time my other hand is free to do whatever. One thumb up since the other one is busy clasping the mouse!