As EaStBeAsT would of said, "diddy is a beast". Those banannas must be the best projectile ever as they make combos in Brawl more than possible. They're excellent for field control, and although you can only have two at a time, they're technically infinite.
Not only that, but unlike what most people say, he has good KO potential with his F and B-air, a good spike in his D-air, and great KO power with his prioritized D-smash, and double hit F-smash to break through sidesteps.
He's also quick, and combos very well, even without the banannas. His recovery is sub par though, it's easily spiked and hard to control.. Aside from that, he excels very well in virtually everything though. He weighs a good amount for his size too. I can't remember what tier he's in(he should be high IMO!), but he's a crazy good character in the hands of a pro.