I know it was already talked about some years ago, but I still want to bring up changing music (there is a better words for this but it eludes me right now) in Gen V.
The musicians are probably the most well-known, but there are more. Some routes have instruments added depending on the season, some percussion is only present when you're actually moving and in certain caves the lower levels will change both the tempo and pitch.
To some it might be just minute details, but I really enjoy it.
Fitting also since Gen V was the last Main Game to use soundfonts (which make this sort of thing easier to do)
I think the most commonly used term is "Dynamic music". Either way, I completely agree with you. It is just so amazing in every possible way. I have made an in-depth post about this in the past, as have my friend DrumstickGaming, our posts on the subject can be found
here and
here.
On that note, I like how S/S also has a bit of dynamic music since the Gym Leader theme changes when the battle is down to the Gym Leader's last Pokémon, just like in Gen 5. I didn't know that the music changed to be more poppy or muffled when a Pokémon gets knocked out, though. Never noticed that when I played Sword.
As for the guitarist in Mezagoza, I have completely missed him... or I can at least not remember encountering him. I'll have to go find him the next time I play Violet.
To add something of my own to the thread... I like the
Pokémon icons used in Gen 1-2. I think they are really charming. Gen 2 especially, because of how many there are. Some of them are very specific, being used for just one or a few Pokémon. Some aren't all that suitable for the Pokémon they represent, like the Marill line using the Jigglypuff icon, but I like it anyway because it just makes things funnier. But even if I like these icons, I prefer when every Pokémon species has its own unique minisprite/icon. That makes it easier to see exactly which Pokémon it is without having to look at its name... but if they are nicknamed, that doesn't always help either.