Trouble with the M1 series is the tank is a) too heavy and too fuel inefficient. The former makes for serious problems with strategic deployment, as well as battlefield mobility--you need at least a class 60 bridge to handle an M1. The latter is probably an even more serious problem, creating serious logistical headaches. I know the U.S. is replacing the gas turbine engines on at least some of its M1s with far more fuel-efficient diesels.
Now, having said all that, in actual combat there are very few tanks that can stand up to the M1. The Leo 2 is probably one; the Leclerc is another (a fine tank, that). Not sure about the T-80/T-90, though.
Dave L.