hey i like these a lot - they're a little on the pale side, and probably a little too outline dependent. I'd push your palette, and maybe add a shared highlight value to help these little guys really pop. I edited your dino, since dinosaurs are AWESOME:
rawr! The only things I changed were the palette, the heavy outlines in some areas, and I added a couple of highlights here and there with a new color. the vast majority of the sprite's actual pixel positions are untouched - but look how much more this one pops! and without overusing outlines!
When you're working at this size, especially at 1x zoom, you can get away with some huge jumps in your ramps, and really you need to in ordder to get the sprite to pop out. The clothes on the orange street fighter guy are just right in that respect - actually those top two street fighter sprites both do a pretty dang good job, but it falls by the wayside on a lot of the others. The only reason that you might want to eschew outlines a bit at this resolution is you don't have much space to begin with, and they really do chew up pixels, when you can frequently use them to add more color and volume information. Also they can have a detrimental effect on the the apparent contrast of your palette. Nice stuff, hope this helps!