All the T-90 is actually would be a improved T-72S (Shilden). Because of the unfair assessment that the T-80 and T-72 recieved during the Chechen and Iraqi war the Russians were having a tough go at selling them, so they changed the name to T-90.
The T-80 used to be the premier tank for Russia and they have only in a more recent short period of time offered it to other countries, with that said after the break up of the former Soviet Union, Russia was left with the main production faciity for the T-72 located at Nizhni Tagil, they have been able to get the T-90 on par with the T-80, plus the T-90 is cheaper to build. This will be their main battle tank until they decide to mass produce their next generation vehicle.
A T-90 or T-80 may not be better than a M1A1 series tank, but Russia has closed the gap.