Oh man, so good. The atmosphere, the graphics, the sound, the game loop... all top notch. I kept wanting to go one more time, and eventually ran out of things to buy in the shop. Nicely done.
I did run into two very minor bugs - the first is if you're in the shop or the fishdex and hit S then you instantly drop your hook, but the "fish again" menu is still on the screen (no biggie, it can easily be dismissed). The second has something to do with the way the lightness/darkness as you descend - in a couple dives the light level changed quickly, which made me think that maybe a tween was being destroyed and reset (not at all sure that is what's happening, but that's the sort of effect I was seeing).