I have owned the CLK 350 CAB, a 550 CAB, and now upgraded to the CLK 6.3 AMG. This car is exhilarating--the engine is amazing, the suspension is almost perfectly tuned--it provides a nice balance between a firm, sporty ride without beating you up, it has back seats that are actually usable, and it flat out goes! I have a few minor gripes-- for a car in this price range, things like NAV, Xenon lights, etc. should be standard. Gas mileage is poor in the city, but surprisingly not bad on the freeway--I average over 24 mpg cruising at 80 mph. Drive one and you will likely buy it--if it's too pricey, opt for a 550, but get the sport suspension--it makes a huge difference.
The engine, the suspension, the comfortable seats.
Better NAV and stereo; xenon, keyless go, and NAV should be standard, not high-priced options on an already over-priced car.