Hello! Thanks a lot for your feedback! I'm glad that still enjoyed it :) It's a good thing that you mentioned the tutorial. I was thinking about it and now I know that it's needed. I probably won't make a special level for it, but instead some short descriptions for newly acquired building parts.
The "special walls" are actually just regular "rocks", but with much more health and a fancy animated texture. The "weird tube" is a time accelerator and it makes everything in the game except for enemies movement 10 times faster.
I was also thinking about adding some lore to make the objective clearer for the players. I have a general idea about a story so I might implement it in the next update.
I hope I provided some explanation for how certain things work and thanks again for your feedback. I will surely improve this project in the future. Cheers!