Hey there beautiful people of the SKYE team
Here is my feedback after completing all the current available missions and roaming around for about half an hour.
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The greatest strength of the game is undoubtedly relaxation. 
Slowly exploring the island with colours that are easy on the eyes, soft brushstrokes on every surface, tranquil music, the soft hum of the propeller, and the lenient controls all add to that goal. And leaning in to this exploration element is undoubtedly the best course moving forward.

That being said I do think the flying itself, although controlling well, is a little bland and could be improved immensely with just some small changes.
A gradual FOV change as speed increases, some subtle wind lines on the edge of the screen, and wind trails emitting from the edges of the wings (similar to the satisfaction the particles that appear when landing on the water give) would have enormous impact on the general feel of the game.

Apart from story related exceptions, I think not having to fly back to base to receive a new mission would greatly improve the pacing.
Perhaps the mission menu can be accessed by just landing.
Also not having to fly to the starting point of races and instead teleporting the player there would likely improve pacing as well (also making the initial direction clearer. I approached the first race from the wrong direction confusing me for a while).
Giving the pause menu a different soundscape or at least stopping the sound of the propeller would make navigating those menus more comforting too.

Allowing the plane to land on surfaces other than water would would make exploring some of the currently uninhabited islands far more rewarding, letting players just stop and smell the beautiful white flowers (letting the player move the camera around with the right stick when landed would make that even better).

Although understanding their function for development, the purple columns were distracting. A poorly mapped or unpolished texture would be more desirable in a posted build while keeping them purple for the dev builds.

And here are some nitpicks:
Some subtle variation in colour for the ground (but mostly the grass) would make the islands look less bland while flying by.
Showing the amount of binoculars/telescopes that exist would make collecting them a more satisfying task.
The roaming boats and planes also make flying around more comforting, and giving them some form of collision would ground them in the world even more.

I hope my feedback was helpful, and I wish you all the best of luck!