LogFAQs > #947477050

earlier gens:
HMs - definitely the worst in first games because you had to manually go to the menu, select your Pokemon, then use every time. Also, there was no Move Deleter so if you taught your Zapdos Flash or something, it's there forever. Gradually changed to make it more tolerable like adding the move deleter, allowing you to access the HM from world screen, making some areas with necessary HM usage to be optional, etc. before removing them altogether in gen 7 (iirc).

Single-use TMs - this was hands-down the worst thing about Pokemon games for me because I liked using multiple Pokemon and with single-use TMs it meant that if you wanted to use a below-average Pokemon for fun, you wouldn't be able to have "best" versions of your good ones. like obviously everyone who could learn Earthquake would want it but because it's a single-use TM, but if I taught it to my Arbok, that means my Nidoking could never get it. Breeding in later gens would somewaht help with this but that meant you still had to plan out breeding charts to make sure everyone was in compatible egg groups, etc. so i'll always love Gen V for introducing reusable ATMs.

forced bloated cutscene/story direction - while a bunch of the older complaints have been addressed in newer games, this is one issue where it's primarily with the newer games. like if you wanted to reset for starter nature, you would have to sit through like five minutes of stupid cutscene bullshit every time. like i don't relaly give a fuck abou tthis girl and her stupid bag pokemon. who gives a shit. let me skip it. your "rivals" getting lamer is also a thing, like how in one of the later ones they don't even reach the final form for their starter.

oh and how Pokemon following you around didn't return after HGSS until Let's Go

i have more complaints but they've mostly been addressed by later games like making breeding easier, making natures & IVs more controllable, etc.

the best changes though are on-screen wild encounters and reusable TMs for sure.