She needs a check-up from the neck-up.
 
I’d like to be able to say that the face, by itself, is okay, but Rainbow Dash isn’t likely to be the sort with full lips of that sort. Further, the nose seems… off somehow. The eyelashes are a bit pronounced, considering she’s more an athletic type than one to fuss with makeup.
 
From the neck down though, it’s dynamite! The outfit suits her, the figure is lean and athletic and the expression on the face, one of determination, is just fine.
 
If you (The artist) gave her a pony face or even just changed up the human face (Supposing you’re going for the EQG aesthetic) then I think you’d see a marked improvement.
 
Just your friendly neighborhood eldritch abomination (Me) dispensing some artistic advice ^_

@C Money  
the fact that she has a nose and lips but hooves

ROFL XD

HELL HAS A FACE.

Everything looks great except the face. (no offence)

@graffiti  
It’s the face… Maybe she fell off the ugly tree, hit every branch with her face, then got got abused by her unknown mother who whacked her face with an ugly stick. ROFL!

something about this doesnt add up