Played all night. Now I'm about to tackle Stone Tower Temple. I just have one Heart Piece left to get in Termina; the other four are on the Moon. Along with the final Heart Container from Stone Tower Temple, I'll have all 20 hearts.
Great Bay Temple is fantastic. Seriously my favorite water-themed temple in the Zelda series. I don't find it tedious at all. It's actually rather linear in progression. Once the water starts flowing in the opposite direction, it's still easy to get back to previous rooms, since there are two paths flowing into the boss key room, and you can access previous rooms from there. Very useful for getting back to the frog with Don Gero's Mask on the same cycle I beat the dungeon. I also love the general aesthetic (glowing pipes!), and the use of the elemental arrows to freeze and thaw out the water spouts, and to create stepping stones out of water (and enemies).
The new and improved Gyorg is infinitely more memorable than he was in the original. However, his second phase seems a bit RNG-dependent. Sometimes it takes him a while to start inhaling. It seems that in order to increase the chances of him inhaling (and you then doing what needs to be done), you have to position yourself near certain objects, and if he sends out his minions, quickly step in front of the object to shield it against the minions. Then you need to roll back behind the object and be ready for when he inhales.
All in all, it's an amazing battle, though. But I think Goht is still my favorite. Looking forward to Twinmold!