I have a bit of critique, mainly concerning the anatomy of the first piece (the guitar guy). I made an edit, which I hope you're cool with:
One major thing is that figure seems too stiff. It's strange, because your second piece doesn't seem to suffer from this so much. In fact,, despite the chibiness, I think the second piece is far more anatomically accurate (as far as such small pieces goes, anyway). I moved the legs and arm into a (hopefully) more natural, relaxed position. I think the arms, too, are a bit too short, as I lengthened them by a couple of pixels. Otherwise, I think the main change made was to the palette. I unified it a bit, reduced the colour count, upped the contrast, etc. Since you were leaning towards the whole "blue shadow" thing anyway, I went ahead and made it more prominent. Oh, and I straightened the guitar a bit.
I'm generally a fan of small pieces, and I like these quite a bit. I just think they need a bit of tweaking here and there, and they'll be pretty great. Good stuff.