By responsiveness, I mean it takes only a light touch on the steering wheel to move it at low speeds, and a light touch on the throttle to get an impressive feeling of power.
They have a lot of steering lock, which means that you can turn the wheels pretty far to the left or right, allowing the car to be very maneuverable for it's size.
As for power - well, my daily driver is a 76 Toyota Corona. The Corona has the same smooth, comfortable ride as a Benz, but boy does it ever take a while to get moving, and it's very hard to maneuver at low speeds, like in parking lots.
My other vehicle is an 83 Kawasaki GPZ 305 - a very small displacement motorbike. It's very torquey, and from a standing start it can get up to highway speed very fast.
But once you're at highway speed, that's about as fast as it's going to go. If you find yourself riding abreast of an erratic driver in the lane beside you, with someone else behind you, you might want to accelerate away from them. As quick as the motorbike is at low speeds, it will take more seconds that you would like to drop the car beside you at highway speed.
In the benz, you can tap the pedal and pass like the other cars are standing still. And it still gets going from a standing start faster than most other cars on the road.
For the record, the car I'm thinking of when I say "the benz" is a current C300, or maybe a C63.
Some people describe a car to be fun to drive when the performance of the vehicle matches their preferences. That is why you have a segment that enjoys Ford Mustangs for their straight-line acceleration (and calls them fun to drive), and you also have another segment that enjoys the Mazda Miata for its sport-tuned suspension, short tranmission gearing (which allows the engine to stay on the powerband with less effort), and low weight (and also calls them fun to drive).
There are a thousand different ways that a car can be fun to drive. Some are not even related in any way to the actual car, but to the sentimental value that the owner puts on the vehicle.
The most fun to drive car I've ever had was a sub-compact that barely had eighty-eight horsepower. Yet it did not consume much fuel. Such attibute pushed me to find how far I could go before needing to refuel. That alone made the car fun to drive.
The Mercedes owner above values the rich set of features that his vehicle has. He seems to enjoy knowing that his vehicle is highly equipped to whithstand and accident, and is even able to reduce the chances of one actually happen. Plus I bet he loves driving past store windows, and see himself driving such a fine automobile. I know I would. =)
I think you meant subjective ;)
The more languages one speaks, the less one speaks one.
I like fountain pens. I process using a good steel or gold nib as a sensual satisfaction similar in degree (although not kind) to a good backscratch. Some pens are fun to write with. Some ... .
I have a 2000 Mustang GT.
If you punch the throttle you hear a monster come out of the engine and set you back in your seat, you get this interesting feeling in your chest as you rapidly gain speed, and when you finally let off, the strangest thing happens: you smile.
Cars that are 'fun to drive' for me (and it's a very subjective thing) are cars where I feel like I am a part of the car. As a driver, I'm encased in the vehicle. It does what I tell it to, how I tell it to do it. It can take corners just as fast as I like them; and I can feel the g's inside the corner.
tl;dr: I feel like I am the car
Basically, the car should "feel" responsive. When you change what you are doing (i.e. accelerating) it should respond with a lot of gusto. The trick is, not doing this when the driver doesn't want it.