Mei's super underrated, by far my favorite character and IMO is on the par of a jack of all trades. Her damage is good, if she gets in range of a tank they get shut down completely, she can take a 1v1 vs nearly any character in the game with the wall acting as an assist to force a 1v1 situation. Her self heal's useful and her wall on top of being able to be used aggressively can wall off potential flankers or shut down pushes/ults/etc and even save teammates.
Anyways, my tag is Nature#1679, feel free to add me.