Basic idea? Awesome.
Art? Very well done.
Should Valve do female versions of the characters? Shoulda done it YESTERDAY.
MY ONLY PROBLEM? The designs for some of them.
The BIG thing about the TF2 character designs is that they're VERY visually distinct. But (and this might be my lack of experience with the game, though it's not zero) the Pyro, the Scout, and the Sniper look VERY similar to each other at first glance. Sure, after some study, you can tell them apart, but you don't have time to appreciate the subtle deviations in design in a FIREFIGHT, and that's gonna ensure you're shooting at the chick with a baseball bat when you WANT to be offing the girl with the flamethrower before she closes in.
Again, I think these designs are gorgeous and really are something Valve should look at to make half their players feel included. But it needs some work before I'm fully on board.