Very interesting!
I like the story, but I don't understand exactly what the illusions are in the context of the story. Is it just the scientist messing with the robot? This is not necessarily something to add to the game - you can leave it ambiguous! It's just a personal question.
I confess I played in casual mode with the checkpoints - I feel that having the two options is a good idea, but I'm not sure I'd care to optimize the game for the non-checkpoints mode. Is there a difference in story? In any case, I'm positively surprise as to how well the checkpoints were implemented! I always felt that when I died, I returned to exactly the place I'd expect to return. Well done!
The puzzles are also very interesting. A lot of games have used the mechanic of walls/floor that is visible but it's not really there, but by making it a puzzle game you actually create expectations on the player on where the illusions may be. It's not just trial and error, I actually felt that I could predict where most of the illusions were. And the visual flair of the illusions is very polished.
I wish there were some illusions in the escape sequence!
Great game. Good job!