Meta Knight

Neutral Special Move: Meta Tornado
Once again, I'm improvising the names here. Basically Meta Knight uses the Tornado powerup that has become a staple of Kirby games and can be guided around the stage, dealing damage to any enemy that gets caught in its wake.
Forward Special Move: Meta Torpedo
Easily Meta Knight's most dangerous move. For this maneuver, Meta Knight spins with his sword pointing forward as he skewers anything in his path. This move is damaging, can tear right through weakened shields, and can even kill enemies at high percentages.
Down Special Move: Dimensional Teleport
A directional teleport that sometimes is accompanied by a slash once Meta Knight reappears.
Up Special Move: Take Flight
While not nearly as impressive as Pit, Meta Knight's comeback special has him flipping up into the air and then going straight into a glide, which he can use to navigate himself back to safety. This is also paired with his ability to jump multiple times after his double jump.
Overall Impressions:
Hang out in the lines for Brawl for a little while and your ears will be overloaded with complaints of how unbalanced Meta Knight is. While I wouldn't go that far to say that he's unbalanced, he's definitely a beast with his lightning fast attacks, great special moves, and great comeback ability. His main problem is similar to Pit's: While he's great at racking up lots of damage with his combos and special moves, he has to bring them up to a fairly high percentage before he can deliver that knockout blow with one of his smash attacks.
Diddy Kong
Neutral Special Move:
Peanut Popgun
Diddy's main projectile can be charged for added power and range. Once the peanuts break, the nuts inside can be eaten for health.
Forward Special Move: Monkey Tantrum
Diddy simply backflips forward, latches onto an enemy, beats their face in, and then leaps off. Can be used to spike enemies downwards if you catch them off the edge.
Down Special Move: Banana Throw
Diddy takes out a banana peel and throws it behind him. The banana peels stay on the floor and can even be picked up and thrown again.
Up Special Move: Rocketbarrel Boost
Diddy's comeback special is very similar to Fox in that it takes a little bit to charge up, and can be directed to fly in specific directions. This move is also fairly useful when it comes to finishing off a juggle combo or breaking a Smash Ball, as it can be quite powerful when fully charged.
Overall Impressions:
Diddy Kong was probably my personal favorite newcomer, surprisingly enough. He's fast, has some fantastic throws, great aerial attacks including a spike that looks like a much faster version of DK's aerial forward A, a great comeback with his Rocketbarrel, and just in general is very fun to use.