The Fabric of the Cosmos
I think I've gotten as far as I'm going to get with casually learning this stuff. The barriers to my understanding are getting pretty technical. Although this did get me over the hump on string theory (just conceptually) and blew the doors off of time. The physics of time seem surprisingly similar to the philosophy of Siddhartha. I still have trouble with a lot of quantum physics (again just conceptually). It just doesn't make sense!
There were a lot of pop culture references in this that felt out of place, but also dated the book in a weird way. There's also the obvious dating from some of this science having made progress in the intervening years. Most notably it kept referencing the large hadron collider, which was under construction at the time of it's writing, as the potential answer to several questions. I know some of those experiments have been run and I've seen some talk of their results and their implications, but my "casual understanding" of the science doesn't easily fit the new discoveries into the larger picture.
It's all still very staggering and enticing. I wish I'd kept up with a scientific education through school so I could dig deeper. The universe just seems increasingly crazy and amazing and I wish I spoke it's language.