Hey! FInished the game.
"Oh! Go left!" part almost got me! If I died there probably I wound not replay from the beginning.
You have nice level design for platformers. Spike placement and doublejump usage is great!
I suggest you to add checkpoints (after getting a key(blue square)), after oppening the door etc.
Also to read the text you need to avoid the pickup, or it will dissapear - so you should place it before the item, not above it.