Much to my chagrin, I'm not very good at Guitar Hero, nor am I good at playing the free Tap Tap Revenge 4 app. Wait, I take that back. If I play the easy level of a sample song (shorter in length), then I'm pretty fabulous at this musical game. But, once you give me a full-length song, I don't have the patience to keep tapping.
The concept is pretty much the same as Guitar Hero, minus the faux guitar. You hit the notes of the song, some short and some long, to earn points. As you master songs, you move up levels and unlock new music. This is a fun way to stumble across new songs you might not find just roaming around a record store, err, I mean, in the MP3 store.
I pretty much can't get past the easy rank, but if you are a master, you can work your way up to master within several different difficulty levels. You can also challenge other users to your favorite songs. The app lists other Tap Tap Revenge 4 players who like each individual song for an easy way to battle. If you don't like any of the free music, feel free to purchase additional songs from the likes of Ke$ha, Lady Gaga, Katy Perry, Linkin Park, Bruno Mars and many more.
Overall, this musical arcade app is well-designed and definitely a must-have app on the definition of free alone. If you play it once, it's worth the download.