Best and worst portrayals in the cast
The best portrayals were easily Mike and Alice, for me. Then Marcia, then Cindy. Jan was good in a lot of ways, but the fact that they made her so over-the-top kind of ruined the potential for extreme likeness to the original Jan.
Shelley Long just sounded like Shelley Long, to me. She happens to have a somewhat similar voice and mannerisms to Florence Henderson, but FH also had a deeper, more seductive voice and general demeanor.
All three of the boys were pretty poorly cast, in my opinion. Greg was too perky, Peter just didn't remind me of the original Peter, and Bobby just sounded like any other kid.
One thing that confuses me a little bit about some of the actors' portrayals is that they all seem to skew more perky and goody-goody than the original characters. I know it was supposed to be a parody of how clean-cut the Bradys were, but they weren't THAT clean-cut. Greg could be a bit of a typical teenage jerk, Cindy could be a little bratty and Carol could be a little bossy. But all three of those characters, in particular, are portrayed in the movie as sugary sweet all of the time.