I can easily name a few key criteria/questions:
-Venue rating (Good or bad? Clean and relaxing? Too small/crowded? Weird smells? Etc...)
-TO Rating (Friendly and professional? Complete jerk and shady as hell? Solved and disputes or other issues? Did he seem happy about what he was doing/overall attitude? Did he have people to help tourney if needed? Were there major problems that were not addressed/handled? Etc...)
-Ruleset Ratinf (Good or bad? Any suggestions or legitimate criticism? Unclear rules? Etc...)
-Time efficiency (Did tournament start/finish on time? Was TO focusing on tournament being done or off playing friendlies? Did people report matches on time? Were all TVs being optimally used? Etc...)
-Overall enjoyment (Did you have fun? Would you want to come back? Would you recommend to people OoC/OoS? Etc...)
The biggest problem will be is if the TOs involved will actually LISTEN to the feedback. Because if there is a legitimate issue and someone decides to completely ignore it...then what is the whole point of this besides being an enormous waste of time?
You want this to be serious, treat it is being serious on BOTH sides. None of this "I know better than you because I'm TO" attitude I've seen in the past. If it's for the community's benefit, then LISTEN to the community, within reason of course.