I love the graphics for this one, and the sound is pretty good too, but the controls are horrendous for me. In the end I gave up trying to collect any guitars, picks, or tapes as attempting the jumps would always kill me. Then I gave up altogether on the second level as I found it far to frustrating. Judging by other people's comments though it looks like I might just be rubbish at the game.
I doubt you're just rubbish at the game; the jumping physics and controls have definitely been divisive. For what it's worth, I think it's probably easier to play with a gamepad; but it's also a game which I wanted to make as difficult as possible without being unfair. My metric was that it should be possible for a skilled player to run the game in one life, so anything so difficult or random that it could not be overcome with practice was cut. (The one exception is the final boss, because hey, it's the final boss. It should be difficult for even the most skilled player.)
I tend to prefer Super Mario Bros. style platformer controls (Guitarguy is secretly an homage to Mario--the "flagpole" jump in the third level being the most explicit indicator as such). It seems that many indie platformers prefer inertia-free motion, which allows for more precise jumps but makes the character feel massless. Likewise, the weightier feel of Guitarguy isn't everyone's cup of tea.