Overall I really liked the mountain. The last puzzles were really cool. There was a great stretch of puzzles at the end with the ones that are solved simultaneously, the double one that forms the path you need to walk on, the symmetry floor puzzle where you make the shape symbols through solutions to smaller puzzles and then finally the pillar puzzles which builds on earlier mechanics in the game, while introducing a cool new mechanic just at the final stretch of the game.
I can see why the stuff before that is more controversial though. Thing is, I feel these ones were deliberately designed to be frustrating and exhausting. They are not hard at all. But the game knows that you know that you are close to the end. Your instinct will be to try to push through them as quickly as possible, but the game punishes you for that, as that will make them even harder to complete. There is a meta-puzzle here to which the solution is to NOT rush, and to go through it slowly and methodically. Once you do, you will find them easy to complete.
This meta-puzzle has a second part which comes after you have completed them. These puzzles, especially the flashing ones, were deliberately designed to wear you down. After making sense of that sensory overload, your mind will be like jelly. If you immediately press on with the final stretch of very difficult puzzles I described in the first paragraph, you will be too tired to be able to solve them effectively. Once you have gotten past the previous annoying gauntlet, your instinct is to press on, because you are so close to the end. But the correct solution to this part of the meta-puzzle is to TAKE A FUCKING BREAK. Return the next day with fresh eyes and a fresh brain. The previous section was designed to wear you out for the next section. Don't fall into this trap. Outsmart the game by taking a break.
I don't know, I personally felt it was very cool. Still, I am very aware that I may just be extrapolating my own experience onto the supposed intention of the designer.