I personally think the best matchup against MetaKnight is Pikachu (don't want to say). Banning him would be MK would absurd. Just because you have trouble fighting MK and not being able to read its moves or using him your first time and owning, doesn't mean you should ban him. There are always exploits. Although he does have a speed near characters in melee, You can always beat them.
For Example: I have a friend that plays way better than me in Super Smash. However, when he switched to MK to show how "god" he is, I basically got rocked the first few 50 times I played him. But over time, I learned the moves of MK and soon I learned some ways to beat him. MK is made up of aerials, if you can't fight aerials with him what do you switch to? You play "I love the land" and F*** him over.
His smash moves are fairly weak, but can rack up dmg. Until a specific percentage, then you'll die.
So banning him at this early stage of Brawl, is a bad idea. Soon people will find new moves like in Melee, No one knew Wave Dash, L cancel, Marth Double Fair, till 3 years after Melee was released. Give it time.