Ok I just fought a MetaKnight at a local tournament earlier today. And he was amazing, pretty much excellent edgeguarding, was fast and didn't even give me a chance to breath.
I think that MetaKnight is overpowered, but requires skill to play. He has high potential for those that are good with him. I've played them before and usaully I can deal with them (Although most of the metaknights I play are noobs) , but this metaknight was like pro, he told me he just came back from nationals tournament and he travels to play brawl, :O.
All in all the metaknight won 1st place, and I won 3rd, some game and watch got 2nd but I didn't get to play him.
It was single elimination and all I can say is if your in a tournament, you better pray you don't get stuck with a good meta in the first round, because after that your done.