Good game that you can come back to every few months/years to find a completely different game in its place. I think a portion of those 9 years was wasted on lost code (stolen laptop without backups) and other rewrites but it is fun.

Its main problem is that singleplayer is very lonely without npc interaction. Online play however on persistent servers was a lot of fun if that's still part of it, as was playing a private server with just one or two friends.

It's been a couple years now since I last played but I would recommend if you want to play a zombie game where you're genuinely vulnerable and every zombie is a real threat.