Pokémon Improvements I Loved
X in Menus: Hitting the X button in a menu closes out all menus and returns you to the overworld! You don't always need it, but when you do, it's very convenient.
Low Health Music: Especially at this point, I think everyone is very annoyed with the beeping sound the game plays when your Pokémon is at low health. It was a stroke of genius to play a different song in battle instead, even though the beeping has been incorporated into the song, which is still a little grating.
Dynamic Music: They did so many awesome things with the music in Gen 5! There's the low health song that I mentioned above, music that changes if you're walking vs running, and even NPCs that will add instruments to the song when you talk to them. The Gym Leaders even get a special theme when they're down to their last team member! It's so subtle if you're not looking for it, but it adds so much to the experience.
Poké Marts are Inside Pokémon Centers Now: Enough said. It's 1,000 times more convenient.
Infinite-use TMs: It's so lovely to be able to play around with the moves my team has without feeling like I'm wasting rare TMs. If only they made it so you didn't need a Move Deleter for the HMs, this game would have been godlike. I wish they had never changed this feature in later games.
Speech Bubbles: Instead of having some characters' dialogue in a full-size text box, short phrases will appear in little speech bubbles around the characters' heads. This allows multiple characters to say something at once and it saves a little time, since you don't have to scroll through smaller and more insignificant lines of dialogue. Animal Crossing: New Horizons does this, too, and I think it adds a lot of character to the world without shoving every single line of dialogue in your face. It's a nice time-saver for the little details.
Registering Items to Y: You can now register multiple items to the Y button! It's nice to be able to have even two items at such close reach, even though the game allows you to register up to 25!
Revised Exp. System: I'm definitely not an expert on how this works, but from what I understand, a Pokémon will gain more experience points when it battles a Pokémon at a higher level, and a higher difference in levels will yield more experience points. In Gens 1-4, it was more of a static number that didn't take into account the level difference between opponents. Even from my experience playing these games with limited knowledge of how the system works, it definitely feels a lot better. You're more willing to take on challenging opponents because, if you manage to win, your gains will be a lot higher. I'm not sure if this is also part of the revised Exp. system, but I also felt much more equipped to take on Pokémon that were higher-leveled. My team was between levels 64-67 when I fought Cynthia (whose whole team was 75+) in Undella Town, and not only was I confident enough to try with such a big gap, but I won on my second attempt.
Animated Battle Sprites: I wasn't won over on this right away, especially because I did most of my playthrough on a 3DS XL and the sprites were too blown up. But on a DS Lite or a DSi, they look much better! And they're super charming! There are so many little details put into each Pokémon, not to mention the details that affect every Pokémon across the board (how hard they land when sent out into battle, closing eyes when asleep, slowing down at low HP, etc.). I'm not the biggest fan of the 3D models that are coming in Gen 6, so revisiting the animated sprites in Gen 5 was very refreshing.
Quality of Life with Healing Items: Say you go to your bag to use a Potion. The game opens the menu with your team, and then you pick the Pokémon you want to use the Potion on. Then it stays in that menu and lets you use another Potion on another Pokémon! This is so convenient when I have to use items on multiple party members, which happens often.
NPCs Who Heal You: If you find a Doctor or Nurse in your travels and beat them in a battle, they will heal your Pokémon for you whenever you ask. I've heard people say makes the games easier, which it kind of does, but I'm the type of person who runs back and forth to the Pokémon Center a lot, so it was a nice time-saver for me.
Strength: When you find a rock you can use Strength on, there is always a hole nearby that it is supposed to go into. Not only does this make the Strength puzzles more puzzle-like, but the rocks will also stay in their holes for the rest of the game! I wish they had done something like this for all the HMs. It serves as a great way to mark progress in the game (if there's a rock in a hole, I know I've been here before) and it saves so much time! Pokémon games are usually pretty linear, but there are often several reasons to return to previous areas in every game. Solving an HM puzzle once can be fun, but solving the same puzzle every time you want to access a certain area is so tedious.
More Version Differences: Pokémon's had multiple versions of the same game for years, and while it was an interesting gimmick at first, I think the series outgrew it a long time ago. The games are so similar that you have never needed to buy both versions to get the full experience. One of the biggest version differences at this point is the version-exclusive Pokémon. And with how big the internet is now, version-exclusive Pokémon feel more like a perfunctory feature than an engaging mechanic. Some Pokémon are so rare (e.g., a 1% encounter rate on one specific route in some games) that I think that would incentivize people to trade even if they all have the same version of the game. There are always going to be some people who are more willing to seek out rarer Pokémon and others who don't want to put in the effort. Plus there are shinies people can trade. Or if you play with your friends or family, you might want to trade Pokémon just for the sentimental value. Honestly, I think that makes trading more memorable and engaging than simply swapping out the version exclusives with another person. If the developers really want to keep multiple versions, though, I think the more features they add to set the games apart, the better. Even things that don't significantly change the gameplay experience would be more engaging and encourage people to talk about the games more, like the different versions of Opelucid City in Black and White. Opelucid City is functionally the same in both games, but it's fun to compare the two. If we have to keep the two different versions, I would love more concrete differences like that!
The Elite 4: You can battle the Elite 4 in any order you want in this game. While their teams are all around the same level, which is a bit less of a challenge, you get to decide how you want to tackle it. You can go for the team you have the best advantage against first to make things easier for you, or go for the team you're weakest against as a challenge. My only complaint is that there's no way to tell which room belongs to which Elite 4 member until you go inside.
Saving: At the very end of my playthrough, I noticed that when you go to save there's a little note at the bottom of the screen that tells you when you last saved. That's so convenient! I usually save multiple times in a row because I zone out and forget whether I actually saved or not. Having a little note of when I last saved would have cut down on how often I did that, and I wish I had noticed it sooner!