3rd Gen Underwater

What were your thoughts on the Underwater areas in the Gen 3 games?

While I wasn't particularly keen on needing to teach Dive to a Pokémon, I still very much enjoyed being able to explore the various different underwater areas, and I also really liked the music that played when you were underwater. I'd like to see Underwater areas return in future games, possibly with a Route that is entirely underwater.

it really is such a shame that the underwater areas are more or less exclusive to the gen 3 games. like.... i think there's one or two areas in unova where you could dive, but it's nowhere as much as you could in hoenn, which is a shame. exploring underwater should've been more of a permanent thing. it really opens up the pokemon world a lot more and gives it more of a sense of exploration, imo.

The underwater area is of my favorite inspirations, I'd like to hack the emerald to build a little secret cave for myself underwater!

Btw the islands in gen3 (red & green) and the second map in gen 2 (silver & gold) are my favorites elements as well

I got really fired up when I came to know that there was an underwater section to be explored in Hoenn, and then there's the option to explore another part of Mauville. But I wish it didn't need another HM and wasn't limited to Hoenn and bits of Unova.
I think it adds to the experience, but it wasn't continued.

In short: I wish there was more of it. I love different biomes being represented in Pokemon. I wish you could find more hidden underground caverns or go even deeper down those trenches to find treasure and or weird wild Pokemon.

I got excited when they reintroduced the concept in Gen 5, and just as pumped to hear that it was optional even, so I wasn't forced to teach HMs at all to my team! Huzzah!

I remember when I was younger and played Emerald over and over again because it was the only Pokémon game I had (the two-three year wait between that and Diamond seemed eternal), I was pretty down on the underwater bits. In particular I didn't like how you could dive to other areas and then get confused about where exactly you are (Despite being pretty good at navigating IRL, I'm still haunted by how tough I found Hoenn's Victory Road too).
When I re-played my games on and off in the middle of the decade I found it much more fun - the music is cool, its completely unique to those games and it makes a great contrast with the more land-based Sinnoh games (especially as I'm a stickler for playing my games in order - Kanto remake, Johto remake, Hoenn, then Sinnoh is the only way I do it). Using Bulbapedia walkthroughs may have had something to do with that! I also enjoy it as a short-cut for getting through large swathes of sea without endless Repel usage.
I didn't like its return in Gen V though. Again, perhaps using the walkthroughs will change my opinion, but I wasn't a fan of the time limit - it jarred with the complete lack of stakes in Black / White's post-game.