For £3.99 - you get a lot of content! Sure it's only 3 maps but what you have to look at here is it's fun, addicting and will last for hours. Plus there are hardly any bugs, the unique game-play instilled in this, just makes it even more fun. Also, did I mention it runs on the source engine? Any game that runs on this whether made by Valve or not, is winning and always plays for good and is essentially a good game. For what it's worth, it's addicting and will keep you for days if not months. The only downside is there is not a massive online community, about 20 servers, everyday, but solo with bots is just as good and you can earn all the achievements in this mode as well, so you're not missing out on anything. You can do basically all the same modes, maps and difficulty as well.
It's silly cartoonish graphics and cliche movie-star characters and some dangerous environmental trap kills as well as the fame-stars you get for each kill. There are plenty of game odes too, hunter, death-match, free for all, infection, kill the leader and many more!
This game is a Bloody good time, excuse the pun, and you should certainly pick it up for it's small price!