remove the space between of the middle teeth on lower part the mouth.
fix the eye shape, it's doesn't look like cookie monster at all.
the mouth width is too wide, you need o fix it.
and the position is too low. move it a bit upper.
cookie monster doesn't have a nose, so remove it.
also it's should be full of fur monster, and the fur need to be smoothen.
that's all. also, don't forget to un-mirrored it when you finish it.