I completed it up until the assembler challenges, and I felt the same way as the author. Granted I knew Kmaps, etc. from my uni days, but given the nand2tetris book you might be able to figure it out.
Development still appears to be ongoing on Discord, which is quite active. I think the dev may have bitten off more than they could chew with their last patch promise: https://www.youtube.com/watch?v=38cKko7sViw
Hopefully the traffic uptick from this will convince them they need to at least post a notice talking about what's going on with development.
I got all the way to the final missions where you're writing your own assembly (that you created) to solve various programming puzzles. Only stopped because I got busy with something else and break was over. I def recommend it. Reminded me at the time of Code by Charles Petzold but applied.
(Last I checked the Author was rewriting much of it for performance reasons and to fix up a few gotchas that should be possible with circuits but aren't here - no idea if they still are but that was my understanding before)
Also have a look at MHRD, which is to my knowledge even more inspired by nand2tetris.