Plants vs. Zombies is a game that I wholly advise you to get. Sure, it is just another tower defense game, but it’s executed in such a way that you’ll find yourself unable to ever get away from it (and this comes from someone who is practically sick of tower defense games).
The music is great, it loops but it’s not annoying and you can very rarely tell if it has restarted or not. PvZ has a TON of humor and great characters. Give it a spin (try the demo even) but I really advise you to just go buy the full game.