It was a fun contest and probably one of the easiest event to bring people together. Judging by the participants, it was definitely a successful contest.
In terms of suggestions, once we get to the last 16 you pretty much know your chances of winning, and it's a battle between a handful only.
In addition to the current form,perhaps you can add different contests, like
- have a winner at the end of the first stage from 32 to 16
- reset the contest from last 16 and have another winner
- guess the final 4 or 8 before the first match
- winner for the longest correct streak