Yes I often find that whether a mech does or does not have a face on it's chest makes or breaks a series.
The art was fine imo, it was just that Clamp did the character designs which as you pointed out do make it seem like you're watching Shoujo.
Some of that stuff niggled at me, considering the protagonist was meant to be a genius considering what he achieved in the end, to have him runnin about a school chasing cats annoyed me. They should have made it darker.