SS Tier
Meta Knight - All matches with him are considered even, or to his advantage. B moves can be punished if not careful.
S Tier
Snake - Perfect candidate for chain grabs and combos, one of the worst aerial games in the game.
A Tier
Falco - Poor Up B recovery can easily be gimped. When fighting Meta Knights, it is considered a even match.
King Dedede - amazing chaingrab, heavy weight, powerful throws, good range, good recovery, and a few quick, hard hitting attacks.
However, Dedede suffers from several problems. As mentioned, he is one of the slower characters in the game, having poor horizontal air speed (the worst in the game). His recovery is predictable due to the Super Dedede Jump's slow speed and inability to grab the ledge at all unless canceled. For speedier characters Dedede can be easy to combo and juggle, and a smart opponent can take advantage of the ending lag time on many of Dedede's moves. This is one of his biggest problems, as almost every attack Dedede uses has a large amount of lag. Also, his big character model is easy to hit, making him particularly susceptible to projectile camping and spiking.
Mr.Game & Watch - He currently is the returning character with the greatest improvement in tier placement. This is mainly due to how much he benefits from Brawl's new physics; he cannot be comboed so easily, he himself can combo with aerial strings, and the fact that there is more hitlag on attacks makes his back aerial "Turtle" very good at trapping. His priority and Smash Attacks are also slightly improved.
Marth - his Counter improved, but his standard attack combo is slower, his standard special is harder to hit with, and the range of his sword and grabs is shorter.
Diddy Kong - Bananas, Good combo-ability, His killing power is somewhat suspect, with the most power coming in his short-ranged smashes. This forces a reliance on spikes for early kills. Also, he is lightweight with an occasionally unreliable recovery. These are not major problems, but all Diddy players must be aware of these.
B Tier
Wario - He is one of the best characters in the game due to his superior aerial game, various ways of recovering and different forms of approach, making him a very unpredictable character. For one, Wario has poor range on his attacks, though his deceptive lag patterns help somewhat and his motorcycle can be broken to yield temporary projectiles. The other problem is that his unusual animation coming out of a grab leaves him vulnerable to chaingrabs and infinite grabs. While these issues aren't overly crippling, a Wario has to stay deceptive and slippery to avoid getting nailed by them.
R.O.B - Great Projectiles, He can be juggled because he is floaty, and his moves with potential to kill have considerable start up lag. Additionally, aside from his up smash, his smash attacks are not reliable killing moves.
Lucario - Aura properties with long ranged, long lasting attacks and the ability to build up damage through various combos and juggling as well as good balance in power and speed. Lucario is a character that, rather simply, relies on building and maintaining momentum throughout the match until it can safely kill the opponent. It has all the right tools and tricks for the job, but falling behind can prove problematic for the Lucario player.
Olimar - Quick-hitting, high-powered character, but abysmal recovery keeps him out of the higher tiers.
C Tier
Pikachu - Good specials, excellent smash attacks and tilts, good aerials, and moderate grabs, Skull Bash can be easily punished. Easy to break shield.
Kirby - Good combo ability, solid character choice all-around, floaty, 3rd lightest character, and rather slow.
Donkey Kong - Great range, priority, reasonable speed, and candidate for infinte grabbing.
Ice Climbers - The Icies aren't very good at using their standard arsenal of attacks for combos, normally speaking. With weak throws, small hammers, and slow aerials in general, the Ice Climbers can usually only manage one or two good hits in close before they need to resort to Ice Shots or Blizzard again. With both Climbers present, KOing generally isn't too much of a problem, although their Smashes are actually better at racking up the damage than at KOing.
D Tier
Zero Suit Samus - Zero Suit Samus is a light character, and is nowhere as heavy as Power Suit Samus. Her grab leaves her vulnerable if missed.
Toon Link - He is a lighter character, and his forward smash leaves him vulnerable, as does his grab should it miss. As well, he is somewhat floaty, and his Stall-then-Fall can cause some unwanted self destructs.
Pit - Pit is also easily juggled, his close up game is impaired by poor range, and his recovery can be gimped by disrupting the Wings of Icarus with a projectile.
Peach - her floatiness allows her to be easily edge guarded. She is somewhat slow in running speed, and some of her specials (and aspects of her recoveries) leave her vulnerable.
Wolf - Having a very poor recovery, and a perfect candidate for chain grabbing.
E Tier
Luigi -
Luigi's problems mostly revolve around his unusual mobility. His lateral air speed is the second-slowest, and his fall rate is relatively slow. His traction is notoriously poor, and his ground speed is rather slow (but stop dashing with is like a wavedash). Range can also be a problem against the swordsmen and possessors of a superior ranged game such as Lucario and Ike, as his approach is generally very poor.
Zelda - her horrible combination of defensive attributes (slow, light, tall and floaty), predictable and unreliable recovery.
Bowser - Poor recovery.
Fox - lack of a proper approach as well as bad recovery and edgeguarding cost him dearly
Sheik - Her loss of many of her killers and her chaingrab caused a drop-off in her position.
Ike - attacks very slow and predictable, with addition to poor and predictable recovery.
F Tier
Mario - largely because his lack of any stand-out attribute makes him less impressive than other characters.
Lucas - him being the target of infinite chain-grabs from a Marth, Squirtle, and Charizard.
Ness - Unsafe recovery.
Samus - Huge nerf from melee.
Sonic - Low Priority, and lack of killing moves.
Pokemon Trainer - This is partly due to players being forced to master all three Pokemon play****, as well as a general lack of high-level Pokemon Trainer players. The stamina problem forces a PT player to make crucial decisions about whether to try and switch safely or to just keep piling on the damage and hope for a KO, with the problem being most apparent when fighting as Squirtle. The Pokémon also all suffer recovery issues, ranging from poor to relatively predictable (from bad to manageable: Ivysaur, Squirtle, Charizard).
Yoshi - Shielding is notoriously bad, and very hard to pickup and play. To be great with.
G Tier
Link - Abysmal recovery.
Jigglypuff - Easily edgehogged, recovery somewhat predictable, and easy to juggle.
Ganondorf - Very sluggish moves, and predictable recovery.
Captain Falcon - Abysmal priority, and poor moveset.