The main thing I noticed was the center of balance seemed off, which tends to flatten a character. Once you have the character firmly balance on their feet, they feel grounded and "real".
The other thing is that the underlying shapes seemed uncertain. I know you said you're in the development stage, but that was the other reason these drawings didn't quite have a 3 dimensional feel.
Once you get the underlying structure nailed down, I think you'll have something to build expressions on Hope this all makes sense!
(Also, I kinda thought a dashed line made a friendly/cute seam.)