Everyone I've played as against Marth is relatively beastly, but he's not the unstoppable killing machine he was in Melee.
Still, I think he's probably the highest tier. R.O.B. is also reeeeaally high to me, except that he needs a lot of good timing to fight fast characters with high priority like Diddy and Falco (Fox is actually okay). Wolf is just a beast and his moves tend to be unpredictable. His blaster is also quite safe to use, even if the opponent approaches as you're doing it thanks to the bayonet on its end. He's also got massive priority, excellent aerials, and little ground lag on everything but his fair and dair (his dair isn't used much above ground anyway). He's also really high up. Of course, the usual Pit and Metaknight. Ike has potentially to be extremely good, as does Snake (his minegames are absolutely table-turning sometimes). I feel like Sonic might have potential, but his game is far too shallow to be really effective, and he can be found out really easily if the player isn't absolutely taking advantage of Sonic's ground speed. (foward+b/down+b, cancel into aerials, lather rinse repeat). Diddy's game is greatly boosted by those gorramn bananas, although they diminish quite a bit once the opponent starts using them against him (it's quite funny turning the slipfest around on Diddy players online, who've probably never experienced it before).
All in all, I'm seeing a lot of top-tier material, the vast majority of mid-tier material, and few in th junk pile that are just too weak in several aspects to be worth it (I'm mostly thinking Link in the latest category).
P.S. How could I forget about Toon Link! Oh Jesus, he's amazing. His aerials are so quick and powerful, his boomerang is a billion times better than regular Link's, his arrows are sooooo spammable, and his bombs look reaaaally cool. His dair is no longer the killer it once was (sigh), but it makes up for it with speed and a cool wind-splash effect that keeps enemies away from his if he misses the ground plant (think Yoshi's down+B stars without the damage).
I've also been trying out Ganondorf and Bowser, although I'm sure they'll be near the bottom of the mid-tier list. Bowser's new throw is just a heckuvalot of fun to play, and Ganondorf is a great tech chaser until your opponent realizes what you're doing. Fun stuff.