Well, I think for
The Godfather you actually have an ensemble cast, and he is only nominally the lead. Just my humble opinion: a lot of other actors would have done a much better job, but he managed not to completely ruin it -- although he comes close. The insufferable mumbling really gets to be a bit much by the end. I think
Godfather II is far superior, and he isn't in that one.
As for A Streetcar Named Desire. Yeah. That sucked.
Naah, I’m not too down on Brando. Beats a lot of the crap actors today. A bit of a strange guy, though.