Had some time to read what's been changed and get some gameplay in with the characters I know.
As a day 1 diddy kong main in brawl, i feel his nerfs are not excessive as they indirectly buff some of his other strengths, namely his combo game. While losing the kill power off fair, nair, and uair obviously hurts overall, his combo game is unreal now. And as far as the damage nerfs go, yes diddy will have to get more solid confirms to get to kill range which is now farther away, but the added ability to followup off of just about everything will partially offset this.
Combined with the fact that most diddy players' banana control is not even close to fully developed at this point we should still expect diddy to be top player in the future meta. The dedicated diddy mains who learn the finer points of banana pressure and trapping will still be terrifying. This is basically how it was in brawl with Diddy being a damage wracking god at advantage with an unbelievable neutral which easily opens people up, but lacking the kill power which would really make it overpowered. Overall I am very pleased with his adjustments, they balanced the character well and actually made him play like he should. I will probably be going back to Diddy as my primary.
Sheik's bair KB nerf is significant but since not much else has really changed (...no change to needles? Srsly?) Sheik will remain top tier as well. When vanish mind games become more advanced Sheik will not miss the killing power of the bair sweet spot too much. As sheik I have always primarily relied on vanish mixups for kills anyway.
Pikachu was a sleeper top tier before the patch and has completely flown under the radar, with no change besides an increase to lag after grabbing the ledge. Pikachu's fantastic aerial combo game, great spacing tools on the ground, respectable kill setups and incredible mobility have all been untouched. With the nerfs to Diddy and Sheik Pikachu is no longer behind the other top tiers in terms of dealing damage and closing stocks, while still blowing them away in terms of mobility and versatility.
Her specials are still the best in the game. Thunderjolt does absolute work as an all-purpose projectile, allowing pikachu to both outcamp those she wants to stay away from and cover the approach to those she wants to rushdown. Pikachus with skilled thunder jolt usage can quickly switch between these two play styles at will.
Thunder is a full screen vertical chase in a can that can kill and lead to followups. It can control space and limit the opponent's options at advantage and in the neutral, especially when b-reversed. B-reversed thunder can be used as a broad option select on stage and a safe and brutal edgeguarding tool offstage. T2 is a heavy hit and Thunder is also surprisingly safe when the bolt hits pikachu.
Quick attack safely punishes, recovers for free, and allows pikachu to warp to advantage in an instant. As several people have said in this thread before, QA is legitimately amazing and is perhaps the best individual button in this game for how it can safely accomplish so many things.
Skull bash is the only special which isn't absurdly useful but custom heavy skull bash gives pikachu insane burst kill power that the opponent has to respect at all times.
My post patch top tier right now is Pikachu, Sheik, Diddy, and perhaps sonic in that order. Although AFAIK sonic was nerfed overall and without a killing throw he probably will not be able to quite keep up with those three. And of course it's been two days so we'll see.
Any thoughts on Ness? I feel he is a very capable character who like Pikachu was largely unchanged due to the fact that his meta has not yet been advanced to the point where people are complaining about it. He may be a sleeper top tier too.
Edit: Was monkey flip's KB reduced? If not that's going to be one of diddy's better kill options.