I liked it.
Pros: Great selection of songs, awesome renditions, simple enough to learn to play, put together quite nicely, controls fit (and changable as GameBalance below points out).
Cons: Did run into a few K notes while playing on the '3 notes - easy' mode which caught me off guard (greensleeves song to be exact), All rock songs (only con if one dislikes rock, though if that's the case, why are you playing this?!), not much else to say for cons.
Other: All in all, I thoroughly enjoyed it. I normally dislike X-mas songs, but I did enjoy these. Awesome work, keep it up.