I'd agree with you, Grenache, that MC is not as stable as it used to be.
The problem for me (and the reason I can't post specific problems) is that crashes happen "randomly". I will be browsing the TV Guide, and Boom! it crashes; or I will be tagging some music and Boom! it does it again; or I will put on a Netflix show, and off it goes again.
None of these crashes are reproducible. They just happen as random one-offs.
I have 3 computers. Looking at the Reliability Monitor in Windows, I can see MC has crashed at least twice in last 14 days on all of them.
Taken together, the MC18 one-off crashes are more frequent than in previous versions, leaving MC18 "feeling" more unstable.
However, I can't oblige JimH in posting specific problems, because I don't know where to even start describing what could have led to the crash!
But maybe that's a good benchmark for stability. How often does it crash for everyone else (according to the Reliability Monitor)?