I think there are a few things to consider here. One is absolute positioning on the tier list. It's kinda hard to argue some characters got nerfed if their tier list position stays relatively the same. For instance, Falco changed a whole lot, but I wouldn't say he was definitely nerfed or buffed, given his tier position remained basically the same (I think he is third best, behind Snake and MK, and now #1 out of the returing Melee cast). The things he lost that made him great are also things everyone lost, which should also be taken into consideration. I would say Brawl has been mostly neutral to him. He dropped in the overall tier, but he finally outshines all the old Melee cast.
I mained Doc and Falcon in melee, and I have to definitely agree Captain Falcon has been nerfed horribly. It's like Sakurai had a grudge against him or something. It's like they wanted to make all his moves so bad that they want to make you try Falcon Punches in desperation. Like someone else said though, the physics changes seem to have hurt him the most of any character, as he otherwise remains almost unchanged. Nothing works right anymore, and he seems to have nothing going for him now. To quote someone else in this thread: “Falcon got a line drive straight to the nuts with the nerf bat.” They should just rename him Craptain Falcon.
Samus, I don't agree with as being a major nerf. Granted, I wasn't a Samus main, so my opinion should be taken with a grain of salt, but Samus seems about as good as she was in Melee to me. Yeah, lack of wavedashing hurts her spacing a lot, and he nair is worse, but I've played some decent Brawlers who main Samus and her zair game is really good. She also can still missile cancel. I would say a nerf, but not a drastic one.
Fox, on the other hand, is hard to say. Definitely a nerf, no matter how you look at it. But Fox is still one of the better characters. All the amazing waveshining and flashy stuff are gone for the two Space Animals, and in exchange, Fox basically got nothing at all (unlike Falco, who got chaingrabbing, laser-locking, decent smash boost/DLX cancel, and a kept a modified SHL spam game). Given the level Fox has fallen, I would say this is a pretty hard nerf, though not on par with the Captain Falcon nerf.
Luigi, minus his amazing Melee wavedash, has got an all around buff, as far as I can tell. Literally everything about this character seems better to me, and he is my new Doc replacement. Luigi definitely got a buff, while Mario got a nerf. The cape no longer is the amazing move it was in Melee, as people can grab the edge backwards now. The FLUDD just seems really stupid to me, even if you can edgeguard (some) with it, as the cape was a much better edge guard in Melee. Lack of L-canceling the fair makes it a really terrible move now. In my opinion, a worse nerf than Samus, but not as bad as Fox, or anywhere close to Captain Falcon.
GW is a demon now. Like Luigi, nearly everything seems buffed (except the dtilt, and only a slight nerf there), except way more of a buff than Luigi got. GW went from low/bottom tier to a top spot on the high tier. The Key is nearly unpunishable now, as it keeps hitting even after he lands. His bair is an amazing move, also nearly unpunishable. In a game where projectile spam has become a much better tactic, GW can put the fear of God into any would-be spammer that relies on an energy attack. His fsmash hits way harder. His throws allow him to tech chase like crazy. His recovery is awesome with auto sweetspotting. GW definitely got the greatest buff of all the characters.
Ganondorf is a lot like Falco, in that so much has changed about the character, it is hard for me to say exactly how much he was nerfed. As a Falcon main, I did my fair share of playing with Ganon, and the new Ganon is just completely different. The f-air just sucks now, and I still prefer the L-canceled Melee d-air to thunder stomping. His side-B is definitely an improvement though, especially given it's suicidal capabilities. The new jab is vastly inferior in my opinion. One of the ways I punish spot-dodges in Brawl is spamming the AAA combo. With the new, slower jab, people can still spot-dodge and punish you. The only thing Ganon seems to have going for him over his Melee counterpart is a better side-B with suicide capabilities. He now plays like a much slower, inferior Ganon, though somehow the nerf doesn't seem anywhere near as bad to me as Captain Falcon's. Overall I have to say this is a strong nerf.
Donkey Kong definitely got a significant buff, while also remaining basically the same character. His Donkey Punch has super armor frames, his f-smash kills very quickly, his ftilt is amazingly effective against practically everyone, and his aerial game is definitely better with his bair. DK can also apparently easily kill people now with his stage spiking throws. His down-B even seems useful now! The fact that DK still seems overall the same also makes it much easier to pick him up and start immediately playing very well with him. A great overall boost, better than Luigi's, though not as good as GW's.
As for Zelda, I hardly ever played her or against her. But she definitely got a major buff in a few departments. Din's fire is now an incredible move, and I don't know how many times I've cursed her up-smash. It literally sucks you into it, and KOs pretty well. Her u-air is also a lot better now, but overall, her boosts don't seem as nearly as powerful as GW's to me.
Those are the characters I've had the most experience with in Melee and whose changes in Brawl seem the most significant to me. I know I'm leaving out Peach here, as her nerf is nearly comparable to Captain Falcon's in terms of tier list droppage and overall crap she has become, but I didn't play with her much in Melee and not at all in Brawl. Everyone else seems mostly unchanged to me. Pika got an awesome downsmash and QACing. Marth seems overall slower, even taking into account this is a slower game, but he is still a solid character. Ness got a slight boost, but is outshined by the newcomer Lucas anyway. Bowser is much faster now and can suicide, but is still Bowser. Jiggs, Kirby, Yoshi, Ice Climbers and Link basically feel like the same characters to me, minus the Melee physics. Sheik is definitely overall worse for worse, but again, not a lot of experience for me with this character in Melee or Brawl. Sheik also seems to have some interesting new ATs that could potentially help her, so I don't think she got hit as hard as Captain Falcon and Peach, probably not even Ganon.
