Just test drove a C300 Sport today myself actually.
The car was a dark silver (Palladium Silver according to the brochure I recieved after the drive) with grey leather and dark grey wood (Black Birdseye Maple). From the outside, it looks great. In fact, I find it to be the best looking sedan in its class. There are a few too many lines going on, but the sharp creases give it a very modern look and the way the light reflects off of it really makes it stand out. My one major beef with the external design is the nose when it's viewed from the side...it's a stub; looks like someone punched it in.
The interior was equally impressive. I've been given a chance to really compare it with the outgoing C class. To sum it up: A huge improvement in every way. The leather is comfortable and feels good to touch, especially the steering wheel's. The COMAND screen folds away with the push of a button (I really didn't bother with it that much tbh), and that alone makes it so much easier to focus on the road. The steering wheel is a little on the large side for me, but it's not that big of a deal. The seats are very comfortable and adequately supportive.
The ride itself is an improvement over the previous C, both in comfort and in stability. The steering is a little light, but on-center feel and overall feedback is a definite leap over the current C.
Power was a little on the small side unfortunately, but it was very linear.
All-in-all I'd rate it 8/10 in its class. Not bad at all.