Thanks for your detailed feedback. :) Having the bosses be puzzle based is an idea that hadn't occurred to me. It seems obvious now I'm hearing it, and I wish I'd have thought of it.
I'm glad the time spent testing and fine tuning was evident. At first, I wasn't sure whether to prioritise that or adding more content, but once I saw the ways my friends and family were breaking earlier builds, I was happy I prioritised testing.