I had a bit of a slow start but things picked up, and I will fully admit it took me an hour or so to finally get to Grub Heap.
My bug notes are pretty close to LTKMN's,
- Closing the periscope always resulted in the player controller refusing to move; I assume you're just forgetting to re-enable it somewhere.
- Unusual jumps when traveling occasionally shift islands and smoke signals.
- The player controller WASD was a little sticky- in that letting go of a key would result in a short delay before it actually stopped, this made walking something of an unusual chore.
I really did appreciate the pacing, very meditative, relaxing sorta chill Myst-esk puzzle thing going on, and it was really lovely, obviously sound in a few places will go a long way, just as LTKMN said with the balloon handles, I honestly didn't know what red was controlling until I happened to see the movement above me.
Perhaps the 'use' distance on some of the balloon controls was a little short, a number of times I'd be reading one of the dials and look back to lower or raise the balloon, only to fall short of reaching them and have to scoot just a bit; minor but persistent enough to note.
But honestly I'm really pleased with what I've played, it's paced wonderfully, very relaxing and with just a little bit of polish I can see it coming into it's own really easily.