Yeah, the difficulty curve in this game definitely needs a reassessment. Level 3 in particular stands out poorly for introducing three mechanics, all of which are required to beat it, instead of giving them one by one.
I can also see how some elements were difficult to tell apart from their anti-matter counterparts (especially mercury).
I'm glad you still enjoyed the mechanics once you did learn them, I'll keep your (along with others' verbal) feedback in mind if I end up revisiting the game.