The Steam Daily Deal for 5/21 is the casual puzzle game Peggle Nights by PopCap. It’s 50% off.
- Peggle Nights = $4.99 / £3.49 / € 4.99
The game has a 76/100 metascore. You can get Peggle Extreme for FREE on Steam if you want to see what the gameplay is like. Look in the Free Games post for more info. Warning: It’s addicting :P.