It's actually the iPhone to blame.
I have a T-Mobile Galaxy S2 and MMS video sent to me via my friends iPhone is horribly compressed with a lousy frame rate.
So, it's not the Sensation at all.
Sorry to bump an old topic- I have my old Sensation that I may use for a backup phone, just afraid to do so reading all these nightmares from the ICS update. Guess my tiny little Sammy Dart still has that spot as its stable despite being on Froyo. :-[