I bought it for $5 last summer when I found it in a bargain bin and I loved it, it was full of poop humor and lacked innovation but it was just stupid fun, don't know why people hated it so much. If you want to have fun, with a game that plays similar to old school FPS games, then you'll like it.
Yeah, I played the demo when it first released and didn't like it at all, eventually got it though PS+ and decided to give it a go and was really glad I did. The gameplay is very standard, nothing special about it, but the more you play the more you want to continue, the story is good and there's just something about it that pulls you in.