Harrow the Ninth, Otherwise Known as WTF Did I Just Read?

I loved, loved, loved Gideon the Ninth. It was dense, confusing, and moved at light speed, but it was so much fun, and at the end, I basically thought I understood what had happened.

I think I also love Harrow the Ninth, but... I think I can say with great and heartfelt conviction, "I have no idea what the fuck just happened."

I mean, I do have some ideas, and some stuff was laid bare, but I am so confused.  Especially by the ending.

So, in comments, if you have read this, please explain things to me.  I am not a careful reader, and I think that HtN might well have benefitted from a much more careful read.  Some stuff I've seen on Reddit suggests some really complicated and interesting stuff that I just plain missed.

Obvs, the comments will be filled with spoilers, assuming anyone is kind enough to explain things to me.