Every once in a while, you have to drive a different car. Really makes you appreciate the M5.
We just got back from a vacation where we had a Pontiac Bonneville rental. This is a car that has NO engine braking. It will do 30mph without touching the gas pedal, and bleeding even a few MPH off at highway speeds means touching the brakes. (I solved this partially by leaving the auto in "2" all the time.) No steering feel, and no sense of center, lousy seats, and pretty gutless for a "sporty sedan."
Also when I had the car in the shop the other day I borrowed a Z3 for a drive since I hadn't driven one. Definitely fun - but (this was a '97 2.8) definitely felt "cheap" compared to the M5. Steering is really quick (good) but has almost no feel (bad). Gearing is low so initial acceleration is good, but lack of torque is quickly noticed.
Anyway, all I know is that each time I got BACK into the M5, it felt SO good.