I agree that MMT is a mixed bag in stereo. A couple of the songs sound pretty bad in stereo, like "The Fool on the Hill." The ocarina is the loudest thing in the mix.
"Penny Lane" sounds pretty good in stereo, though, as does "Hello Goodbye."
The White Album is definitely better in stereo.
In general though, aside from a few cases in which fold-down mixes were used, I think the US mono mastering had a depth, warmth and fullness that you don't find elsewhere.