I have had this game sitting "uncompleted" for almost 1.5 years now, and I'm now throwing in the towel.
Bit.Trip Beat is great fun, and I completed 4 out of 5 of it's levels (which amassed 4 hours of gameplay), but the last one is very tough. It's not tough because it's a challenge, which it is don't get me wrong, it's tough because it lacks any checkpoints, and is literally a 15-20 minute long level. When you reach the end, if you fail, it's over. Start again.
That, I couldn't abide by, as it isn't simply just the mark of a "hard game", it's just very badly designed, as it doesn't make you want to continue playing, it makes you just close the game and stop playing altogether.
A decent game, tricky in many ways, but with ultimately some flaws in it's design. Worth picking up if this is your kind of game, otherwise avoid, as it'll just enrage you!