Thanks so much for your feedback! I've already amended world 2-1 to remove the use of portals.
Level 2-3 has actually become 1-2 (woah what!?) so hopefully that will help remind players that portals are (usually) friendly.
I've made a number of changes to the order of levels along with the next batch of 5 levels that will be in the upcoming release, which I'm hoping to have done soon.
As for the Ghost-Blocks, their timing is very much on the quick side, but due to (some anomalous factor!?) they last longer on the EXE than the web build of the game. If you felt like they faded too fast on the Web build, I agree, and will bump up their timing to compensate.