I really like this one.
Gameplay: 9.5/10. This game keeps me going without ever boring me out. It's not easy, sure, but the difficulty is fair enough for me to not feel like "This jump just is impossible", rather like "C'mon, niffreak, you know you can do better than that!" The only bit are those heart barriers, but those aren't neccesary, so they aren't that much of a deal. It's just my completionist sense that keeps nagging on me.
Graphics: 8/10. I'll give you that, they're not very detailed, but they do what they have do. They really change my mood: from obnoxious to charming to relaxing. There is just the lack of detail.
Music: 7/10. This one variates. The music at nightwalk, for example, is very soothing and sets the mood. Into the next zone, deepmountain, this devolves into a drum and a horrible electric guitar, and so on. It's not too good, but when it's good, it REALLY is good.
Overall: 8.5/10. Bonza job. (Sequel, sequel, sequel...)