I wanted to wait until a large enough alpha to comment on the hack, since problems in the earliest alphas are almost certainly going to be fixed and I feel this is enough.
The main menu theme is far too high-pitched. What's the original version of the song? I may put the song on my backlog and do my own port of it.
The mapping in this region feels rather cramped outside towns. There seem to be a lot of two-tile-wide paths filled with lots of tall grass, as well as water routes and Tangelo Jungle. At minimum, I think changing Tangelo Jungle from having every step be a wild encounter to adding tall grass within the area and only those spaces with tall grass having encounters (basically switching from Ilex Forest to Viridian Forest in regards to encounters) would help a bit; I do think at least a couple routes changing to be more open would go further to fixing the problem, though. The towns, Underground, and Crystal Cave are all mapped well and I don't have complaints.
I also think the wild distribution is rather skewed at the moment. The vast majority of Pok?mon I've ran into so far have been Water, Bug, Poison, or Flying. Even the Normal-type seems a bit underrepresented with only Rattata and Spinda. Even 1-2 land routes seem to have Water-types like Poliwag despite the large bodies of water. Trainer parties are slightly better by having Pok?mon like Meowth and Mankey (that don't seem to be added to any wild areas yet; I'm sure they'll get added later as more areas get mapped), but with all the water routes populated by Swimmers and Fisherman I find myself still fighting far too many Water-type Pok?mon.
The female swimmer sprite is glitched on Route 54 and has incorrect walking frames.
On Sunburst Island, the NPC who gives you a Sharp Beak has slightly glitched dialogue that cuts itself off as soon as it finishes.
Spinda is currently genderless.
There's a minor visual glitch with the Pok?dex, where the uppermost row of tiles is corrupted when you check for area. It doesn't appear on the Town Map, just in the Pok?dex.
I think all the custom sprites in this hack look pretty good, to try and give more positive feedback after all that criticism. The overworld tiles also look good, but I think it could use a bit more variety so the islands can stand out more individually.
I am looking forward to more progress on this hack.