I thought the game was generally well made. The design of the puzzles was interesting. I like that there are very small changes found in the puzzles, while not completely changing the game completely, do add some variety.
I do find the game to be a little on the challenging side. Particularly in the early stages. Maybe design the earlier puzzles in a way that makes them quickly solvable. Move forward quickly in the beginning, and challenge the player more later on.
The biggest area of potential improvement is in the presentation. Work on a theme to wrap the game's visuals around. People tend to be critical of games that do not look good. And people will overlook a lot of things when your game looks great. That could be a source of the criticisms that you hear.
And maybe rethinking the select selection. I find it a little confusing. I'm not sure why it is a wedge shape. Look at how other puzzle games structure there progression. Games like Snipperclips or Three's.