>>28294623HGSS isn't super ugly or anything, though I really don't like how any of the grass short or tall looks. I just much prefer how Gen II looks, both in the general art direction and the GBC color palette. UI too. Even then I prefer the looks of any of the other DS titles to it on its own too.
As for DP, just two little things I don't like that they changed. How you first get your starter, and where you first meet Cyrus. I liked both of those better in DP than Platinum. The first because it was original and stands out as unique in how you get your starter, and the whole Red Gyarados documentary ties in with HGSS which supposedly take place at the same time, and an NPC in the postgame sloppily still refers to it despite the documentary no longer being in the game. The latter because it makes a nice bookends where the first place you meet Cyrus is where you eventually defeat him, at Mt. Coronet. That's all.
BW1's story basically exists entirely to make Ghetsis seem threatening, cunning, and evil. It succeeds in that. However, Team Plasma themselves and the whole pitch of them to the player in promotional material and the first encounter with them in the game are terribly handled. And it never really does much other than the central Plasma plot. Bianca's little subplot with her dad is okay and had a great idea behind it, but they didn't spend enough time fleshing it out. You get her dad freaking out about her going on a journey at the start, she leaves anyways, and you don't hear anything else about it until he pops up at Nimbasa out of nowhere and gives up after a brick of text from Elsea.