Constructive Review
I enjoyed playing around with this, and I'll say first that it has potential, but it was a bit limited and simplistic in some areas .
Your drawings were fairly good, but I would try adding some color and making the mounted toms and hi hat/cymbal stands a bit more 3D.
As far as audio goes, everything was spot on. The sounds were crisp, clean and very responsive when clicked. It may seem kind of boring to some, but maybe add a metronome option the player can turn on/off to use while playing. Also, having an array of guitar/bass riffs from all different types of music to play along with would make this game more fun and take it to a whole new level, IMO.
The one major flaw this has is the fact you play with the mouse. This makes it impossible to keep an interesting beat! Using the keyboard would allow use of the hi hat/ride cymbal with the bass snare and tom drums simultaneously as one would when playing on a real drum kit.
Overall, I'd say that you have a good start. I really do see some good potential here. Please take some of my ideas/criticisms into consideration and keep working on this, I would love to see another version!