>>719657567
It's the Pokemon Orange romhack made by Pia CRT. It is being remade from the ground up under the name Pokemon Orange: Island Walker, which hasn't been released yet. But you can still find the original hack online.

>>719657295
I like it because I think the creator did a very good job turning the Orange Islands into a fleshed out region. I really appreciate when someone puts the work in to make a new region to explore and it turns out well.

Not to mention the cozy Gen II style sprites give the game a warm tropical vibe. Also, the elements from newer games that were added were well thought out, so only stuff that would make sense in an Orange Islands game better got in (like diving).

The subtle variants in pokemon design shown in the anime is a nice touch, and the post game Pokemon 2000 movie storyline where you get sent up on the airship is fun.