Let's break it down:
- She can wall off corridors and entryways with a barrier that has more health than Reinhardt's shield.
- She has a self-heal that makes her impervious to damage. It is better than both Roadhog and Bastion's self-heal AND lasts longer than Zarya's target barrier (you know, the character whose abilities are making barriers). This will also BLOCK enemies' progress on objectives. There is no way to damage this or move it.
- Her freeze takes way too little time to complete. Even dashing around as Tracer, it felt impossible to escape.
- She has both freezing AND sniping capabilities.
- Her ultimate is stronger than most other characters. Not only is it AoE, it freezes AND damages all characters within AND lasts longer than Zarya's.
I like the balance in this game, but Mei is just the stick in the mud who I always found grossly overpowered.