It will probably go on sale for under $5 again during steam christmas sale. But I think it is still worth it full price.
I pretty much stick to lower population servers and have yet to come across a single hacker. I stay away from major pvp places like smallville though.
Imo its a really fun game, just running around looting awesome weapons, killing zombies along the way and some intense encounters with other players.
you can always apply to a clan that has their own private server if you want to do pve only