Right off the bat I'd say you need much higher contrast. At 1x zoom, it's basically impossible to tell that these are shaded. I would use a softer color for the outlines, too (as people generally seem to frown on straight black).
These suffer from the same issue as many other RPG sprites, too. Given that these are (I'm guessing) meant to be top down sprites, the perspective is a bit off. At the moment they appear to be staring straight at the viewer/player/whatever. It's easily fixed (just lower the eyes a couple pixels and maybe extend the cranium one or two) but it's something that should be righted...
I like the gryphon and the twin doggies.
