So I finally got around to actually playing the game after the 1.0.4 patch hit and messed around with multiple characters.
Dedede nerfs aren't as bad as I thought, but I feel like his matchups as a whole are going to be fairly wonk compared to before; characters like Greninja, Rosalina, and Sheik being nerfed helps him out (I *almost* want to say the latter two feel like 55:45 in Dedede's favor now, but that's likely a generous assumption), but vectoring tweaks and buffs to other characters makes other low tiers more threatening; particularly Mario, who actually got nerfed even, is much scarier now that VIing up and out of his combos isn't an option. Gordo nerf hurts against Bowser/Charizard/somewhat Sheik and Megaman is an even more impossible matchup than he already was. New dthrow isn't explicitly worse than the old one until around 80% where the opponent can DI out of followups (he had fair as a guaranteed followup until awhile after 100% before), but I think dthrow>bair might work to higher percents than it used to.
Meta Knight to my surprise doesn't feel much different to me, but in fairness I had the poor luck to only play him against Sonics during my session so I was fighting an uphill battle at all times. I feel like the bair/nair buffs will make quite a bit of difference for him but he really needs his range problem addressed above all else.
I probably overestimated Ike's buffs, but it also doesn't help that he isn't the type of character I'd usually play :V The fair/dtilt speed buffs in particular are quite nice, but they don't magically fix all his problems. I think they magically fix enough of them that he's probably better than half the cast at worst, though.
I'm not quite sure what to think about Greninja yet. Usmash nerf was well-deserved, shuriken nerf was questionable but tolerable, Hydro Pump nerf is arguably a buff because it can actually gimp properly instead of moon launching now, but fair/uair nerfs felt needlessly excessive and his buffs don't feel like they do much to patch up his problems (though air sneak being a viable edgeguard move now is terrific, fair already worked for that before...). I don't think he was hurt as badly as some people seem to think, but I definitely feel like he was gutted more than he needed to be. Rather, I'd be okay with him if shuriken end lag was reduced by 2-3f and uair/fair still had KO power. Usmash isn't a ridiculously broken "use for every situation" type move anymore and his landing lag cancel was removed, those two things alone probably would've been enough nerf for now imo.
Sheik really doesn't feel much different, she just takes a bit longer to do what she did before. Vectoring tweaks might actually result in her being buffed overall in a custom move environment since Pisces/Jellyfish didn't suffer the Bouncing Fish nerf and weaker fair allows for higher percent combos.