I've solved ~300 puzzles (out of 600) but am able to trigger the ending, so I am finished but not 100% completed yet.
I haven't found ANY puzzles where I feel like you're guessing at the solution. Every puzzle I've solved has had well defined rules. I don't want to give too much away, but broadly speaking there are two types of puzzles: Those that rely on the symbols, where whats on the screen in front of you is all thats required and those that...don't.
The first category, you slowly build up your understanding of the various rules as you progress, and they all play by the same rules. The second category though, the real puzzle is to figure out what you're missing, generally by observation.
But once you learn the difference between the puzzles that you can take a face value, and the puzzles where you should look around, it feels much more fair.
The only time I felt truly frustrated was the few puzzles that introduce audio as a mechanic. I think deaf players will be unable to 100% this game because of a handful of puzzles, and theres no indication that the piece of the puzzle you're missing is sound.