I made it through The Secret Doctrine and Isis Unveiled, but I feel like largely it was a waste of time. Blavatsky says a bunch of shit in it, obviously, but most of it is shit she misunderstood from Eastern traditions mixed with shit she is just probably just making up because she never cites any sources or credits anyone properly for any of her outlandish ideas.
It was a slog, and honestly pretty boring. There are audiobooks of it on youtube, go skip around some and see if you hear anything of interest to you.
https://www.youtube.com/watch?v=kg8_eXgPX_k&list=PLQuu3tcfVdSVO_W5FCe8NQVa6lK4pxrFQ
I think I also may have been a bit bored by it because I was already familiar with all of the ideas she was laying out, from having read many other similar and related texts, like a lot of Rudolf Steiner.