To add onto this: abilities. They routinely change up the mechanics of moves that didn't really need it (Wish, Feint, Surf, et al) and I'd like to see more inter-generational ability changes, even when they aren't massively needed. They've done a bit of this recently with the likes of Gallade and Empoleon but it's so rare when it happens. Give Snorlax Poison Heal and Salamence Aerilate as their new HAs! Give Sableye Wonder Skin instead of Keen Eye! Give Hitmontop Speed Boost instead of Steadfast! Idk! Go nuts!
Yeah, having played a lot of the older games in the last couple of years, feeling this a lot. Everything atm seems to get powerful moves, and usually at really early levels. It's one of the things that made ORAS incredibly unsatisfying for me - everything had much wider movepools than in RS and the difference was incredibly noticeable. I felt like I was steamrollering over everything. The range of TMs available doesn't help either: I mean, before the third badge you're already able to purchase Venoshock, Facade, Bulldoze, Charge Beam, Dragon Tail, Aerial Ace, and Low Sweep. I don't like that I have to deliberately not use TMs to maintain a semblance of challenge: part of the challenge of the older games, particularly the first three gens, is deciding what the best investment of that single good TM you have is.
Sneasel is a classic example of something that generally gets quite good, interesting options, just rarely its own STAB. I've just bred one in Crystal and it has a much more competent moveset than I remember - Shadow Ball, Metal Claw, Iron Tail, Dynamicpunch, Slash, Strength, (and obviously Hidden Power to round it off). It even gets Surf if you're absolutely desperate to do a fully special moveset with Ice Beam/Punch and Faint Attack.
It operates differently pre- and post-Gen IV - and obviously generally for the better later on - but I like that there are a lot of Pokemon like this in the first two or three generations which need a bit more thought to their movesets than just, as CE said "90/100 "[type] Slam"+"[type] Beam"+coverage 1+coverage 2.