I have too much music
This is possibly the best thing since iTunes for my music... I love being able to play MY songs, the bands that I like.
It's pretty accurate detection, and the difficulty level is astounding. I need to get a USB guitar, because I think I broke my keyboard already.
The visualizers are top-notch, probably the best i've seen since the early winamp days. I find myself totally b0rking a track because I get distracted by all the shineys.
Kudos to the devs also, they are really active on the Steam site and answer questions pretty fast.
One request: Make a Mac version please!