If you don't know how paid apps work by Tapulous view my Coldplay review here:
Standard Tap Tap Revenge stuff.
This was the first Tap Tap Revenge game to include multi tap and also sustain taps.
Tapulous really wowed me here, I love the look and feel of the game, the menues are sleek and quick and the theme for normal songs is very cool. The themes for Bosses are the highlights of the game, and rightfully so. My favorite is problalby the boss for the Hard difficulty.
Overall TTD is a great game, and great if you like music with a great beat. The only thing i really hate about it is that there is no boss level for Extreme!
Value: Worth it.