40.x was feeling to me more like kind of "development" version in between 2 releases, new systems were put in place and were required for what's next in Toady's plans with the world activation thing, but most of them were breaking things that were fun in 34.11 .
For actually playing the game i still had a lot more fun replaying 34.11 actually.
Now 42.01 has some new stuff that improve over 40.x obviously, the systems are still the same and will be improved and fixed for sure, at least i hope
For the adventure mode there are still too much "it was inevitable" and overall passivity (but i must admit there is a slight improvement, some very rare npc aren't passive anymore) for my enjoyement as i'm not interested in the dance/sing/story new stuff , each to their own i guess, and already saw the other 40.x remaining adventure feature during df2014 era.
Now fortress mode has sieges again, they still take their time, but they come surely now, unlike in df2014 in which you prepared your military for a decade, reaching all of them to legendary status by just sparring a couple of years and the extremely rare gob siege coming were incredibly weak in number and skill (no weapon master or weapon lords in gobs rank, only low skilled troops).
Just the siege potential coming back to me is a big improvement over the broken 40.x and made me enjoying 42.01 so far despite the crashes and other assorted problems.
Hopefully with more bug fixing and tweaking of the 42.x , we'll all be happy to forget 40.x and get back DF out of just some testing things to a more fun experience like in 34.11.