Really, really well-designed puzzle game. The art is lovely, the vibes are immaculate, and the narrative is really cool.

Pros
+ Great visual style
+ Good music, relaxing and doesn't distract from the puzzles
+ A solid mix of "classic" Sokoban puzzles and new ideas
+ Open format allows you to move between puzzles at your leisure, opening up new routes feels satisfying
Cons
- Very small number (3) of puzzles feel a little unfair
- Some symbols can be very hard to see (accessibility)
- Very little story

Isles of Sea and Sky has all your classic Sokoban puzzles. Shoving boxes? Check. Picking up keys? Check. Sliding on ice? Enemy that mirrors your movement? Swapper tiles? Sliding blocks? "Conveyor belts"? Yeah, they're all here. But they also have several new clever ideas, mostly with their elementals.

There are tons of secrets to be found here, many of which are marked with a symbol. However, be advised that if you suffer from vision problems this may not be the game for you because so many secrets are marked with subtle icons. Particularly notes that appear on ice tiles, a couple eyes that appear on dark walls, and one snow tile design.

Some complain that it's a bummer you can run into puzzles without having the tool you need to solve it (it feels a little bit Metroidvania inspired in that way). That is true, but the game does a pretty good job of funneling you with island-specific keystones to the right puzzles first. You can ALWAYS do gemstone puzzles at the start of an island, so focus on those first.

The vast majority of puzzles here feel very fair. Some build up across multiple screens, some share a screen with two or three other puzzles! Many took a lot of iterating and retries but only three of them left me groaning. For a game with ~150 puzzles, that's not a bad ratio.

Great puzzle game. The early puzzles are simple mostly to act as a tutorial, but they can get pretty diabolical later on. Most areas have two or three "goals" that are typically solved separately. This does a great job of automatically adding red herrings to each level - "I can push this block over here and do this thing, but will that help me get the star? Or is that just to get the key I already got?".

The main gimmick is that there's a somewhat-metroidvania approach where you visit different islands and can obtain new powers from each. This means that not all puzzles can be solved right away - this can be annoying, but it means the answer to "how do I solve this puzzle?" is sometimes "I can't - I need to go somewhere else". The fact that every puzzle must have a solution can sometimes be a clue itself, and this approach removes that.

In general I like the powers approach, but there's one unfortunate problem. The game has powerups, and without spoilers, you won't know what they do. But the game also has secret passages - walk into a normal-looking wall and it turns into a passageway. The secrets are telegraphed, and there's plenty of instances of "literally the only way to get up there would be if there is a secret passage right here, and yep." By themselves, the secrets wouldn't be too bad. It's just that the combination of secrets plus the powerups is very annoying. If you run into a puzzle that seems impossible, there are three possibilities:

1. The puzzle is solvable, you just need to think it over more
   
2. The puzzle isn't solvable because you're missing a powerup. You need to leave and come back.
   
3. The puzzle is solvable once you activate a hidden passage.

And there's really no good way to distinguish between 2 and 3. There is a "there's a secret on this level" indicator, but I didn't notice it until I looked at a guide. The powerups add a ton of variety to the puzzles, but the addition of secrets can get really annoying.