Before I bought my beloved w210, I was looking at the 740i Sport Bimmer and D2 Audi S8. If you are also looking at these, stop now. There is no comparison. The W210 is the most capable, dependable and FUN car of them all.
I have owned mine for 6 months now and can honestly say it is the best car I have owned. It is very comfortable (although the Audi seats have the edge), clearly built for cruising an autobahn at 100mph all day long. This thing just chews up the miles effortlessly. I get between 17-21mpg in mixed city/moderate highway commute. Not too bad considering the Saturn 5 rocket performance that lurks beneath.
Motor, motor motor. Its an E55 AMG. Enough said. If you enjoy genuinely 'driving' your car, this car is for you. Almost 400lb/ft of torque is a riot. It is like a 4 door muscle car, with AC and a CD player. (trust me I sold my muscle car for this) It may have an auto, but the shiftable auto is a joy to use. It never hunts for gears in odd situations. A 'soft' ECU reset (google it) guarantees crisp shifts and enhanced throttle response.
It is manually shiftable which is awesome for spirited driving. I love the subdued looks and monster performance. Find a clean, unmolested, well kept one and this 12 year old legend will still be your 'go to' vehicle past 200,000 miles. Not good in snow.
Front seats could be a little more 'aggressive' for my taste. Make a car this capable and you are going to want to push it round corners. The car can deliver, the seats can't really. You find yourself bracing on the door and center console. Rear seats do not fold down, so if you are replacing a wagon or SUV with this, something to consider. Trunk is not as huge as the vehicle size may suggest but it is not terrible.