I've driven the 2013 C300 Luxury for 5000 miles.
It is far better than the older 2011 with the increase in horsepower from 228 to 248 - it really moves now with the 7-speed.
My gas mileage is 21mpg around town and has reached 30 mpg on highway trips (~65 mph).
The exterior is neater and interior comfortable - it is well made and solid.
It has the mBrace system, with Sirius radio, Bluetooth capability, and navigation (which works unexpectedly well).
I accepted a rear camera, that works well but not something I would have normally purchased.
Not too happy with the stop-start ECO feature, but it has worked flawlessly so far (it can be turned off, but must be turned off each trip).
Improved power and acceleration.
Excellent fit and finish inside and out.
Transmission is smooth.
Styling is handsome.
Gas mileage more than acceptable for a V6.
mBrace controls are OK, but still a bit simple.
Steering is slow and muddy.
Trunk is tighter than 2011 (places to hide first aid kit and fuses). Can't fit long golf clubs.
Still has cigarette lighter - dump it.
The central storage compartment has an mp3 and ipod connector that reduces storage.
Glove compartment could use some reorganization to be more useful.
Rear seat area is tight.