Aaargh! I love tower defence games and I quite like Two Worlds 2 (even though they wouldn't send me review code), but I have both Portal 2 to finish and Witcher 2 preview code on my PC. No time! Nooooo tiiiiiime! Maybe you have time. Tell me you do. If you do, you should try the bizarre Two Worlds 2 spin-off game Castle Defense, for which you slip into the shoes of TW2 arch-nasty Gandohar as he smacks down rebellion. The game's not out until May 17, but there's a demo now.
Amazingly, they haven't called it Twoer Defense, but that's because they're not as clever as me. Try it here.