Very well made, quite hard sometimes, but not rage-hard. I'd give it all 5 stars or 10 stars, I honestly can't remember how the rating system even looks like... But if it ever goes live, that be my rating!
Also, it made me sort of nostalgic for VVVVVV, loved this detail! I wonder if you actually were inspired by it? (seeing the "gravity switching <<lasers>>", I think that might be very true.)