Nerfs: Captain Falcon, Sheik, Samus, Peach (In Order)
Buffs: G&W, Zelda, Kirby, Pikachu (In Order)
With regards to some other characters stated:
I'm not sure of what to think on Ice Climbers. All of their attacks seem so **** weak to me compared to Melee, and they've lost the Wavedash and Wobble. But a lot of they Desync combos in Brawl look good, and they've got their Chain Grabs and Alternating Grabs to make up for it. Their recover is also a lot better, and they can both grab the ledge this time around. I'm not sure what to think on these guys.
Jigglypuff wasn't a character of mine in Melee, but I love her in Brawl. From what I can tell, she was more affected by the change in the physics engine than in her actual moveset, due to losing a reliable WoP. Her Fair has a major buff though, as does her Rollout. Her Rest is nerfed alright, but still kills fairly early. I'm not sure here either, but I wasn't a Jigg main in Melee.
Ganondorf is similar to Jigglypuff in the same regard with me, although I think everyone is very ignorant when it comes to Ganon. I think he has the potential to play an amazing game, despite all of his obvious disadvantages. His Forward B is too good, he has a lot of IASA frames on his attacks, he can combo reliably (and kill with those combos), and he can cancel the lag on his stomp.
I don't know why people think Luigi was nerfed. Luigi, despite losing the Wavedash (which is universal mind you), has recieved a lot of buffs. Better recover, more power, better priority. His aerial game is amazing too compared to a lot of characters.
Fox. He is nerfed because you probably couldn't get more broken than Fox Melee was. The nerf to him was minimal in terms of Tier placement, and he will still likely be High Tier, so I'm not sure if he's worth mentioning.