Wow, DeoxysTrainer, that was insightful...
I say the first one is very good except I would've chosen a different color other than pink and it looks like you made a mistake on it's left foot. It looks like a pixel or two is missing.
The second one is good except for the area just above it's right leg. It's all one shade and looks far too flat considering that area would definitely be rounded.
The last one is fine except the flame color doesn't really go with the rest of it, IMO.
I'd say that about covers it.
P.S.: Keep an eye on the angle the lighting is coming from on each part. On the second one, for instance. Nidoking's legs make it look like the lighting is coming from our right as does the horn while the body an tail suggest the lighting is coming from above.