Actually, metaknight is really fast based on the info we've gotten from E4all. And if you don't KO him by sending him flying offside, he's gonna recover.
MK's real weakness is the lack of any power moves. He has a lot of strong attacks, especially his specials, but nothing has a lot of KO potential, even his smash attacks. But that balances with his recovery.
Overall he will definitely be a strong character in the beginning, as he's not terribly difficult to pick up and learn with. Whether that continues will be affected by how much is learned about how to play other characters.