Thank you for the thorough comment!
The difficulty was definitely a bit jagged - the tiles themselves have a major impact on how difficult a level can be. There are two levels which are off-the-charts-difficult IMO, but I put those at the very end of the original and bonus levels respectively, so the user really feels satisfied when solving them, being rewarded with the completion of the game.
The commentary was only intended to be hints at first, but I couldnt stop myself from adding some text to every level :)