Out of the 3 books mentioned so far I've picked up Dragon Heist and Ravnica.
I had the 2E Undermountain box and it never really saw much play. Although from what I've seen (and read on the forum here) I think Mad Mage might be more useful to me. I've skipped buying about half of the 5e adventure books, usually ones I played in, or hoped to one day play in *cough* Curse of Strahd *cough*
If I ever decide to run Dragon Heist I will pick up Mad Mage.
I liked Dragon Heist, but like the other hard cover adventures I've picked up I'm probably not going to get much use out of it, other than a good read. I did like the info on Waterdeep, and the way the adventure is set up is really interesting. I tend to avoid big cities as a DM, so I thought this would be a good resource if I wanted to rectify that.
Which brings us to Ravnica. I thought my aversion to large cities would mean this was going be another book to read not play. Not knowing anything about Magic the Gathering I was interested to explore a brand new setting/world. I have to say, I was really surprised and impressed with the book. It's like a box of ideas to play with, which I find inspiring. It's a jumping off point to make your own version of Ravnica. At times I felt like there's a lot missing, and that I had more questions than answers in some ways, at least in terms of how the planet sized city works. Although some of those initial concerns I did find answers to after a more extensive read.
It's helped that I was a big Planescape fan, and I can see a lot of crossover. I'm even thinking of converting 'The Eternal Boundary' by changing the Dustmen to Golgari Swarm.
Anyway, that's some thoughts on the current releases.
I'm definitely interested in how the Magic / D&D cross over experiment goes, it's probably my favourite book since Volos, so I'm keen to see what's next.