My thoughts on 10 after messing with for the last year:
-Lots of intrusive apps/stuff wanting data uploaded to Microsoft.
You can disable a lot of it, but you can't truly turn it off without breaking some stuff.
-10 REALLY wants to push Edge on you. Edge also sucks pretty hard for a browser.
Edge seems to be built directly into the OS, so if you try to forcefully remove it, it'll cause problems. Or it'll just pop right back up!
Also, I noticed for the 1703 update if you're still using IE11, they added a button so you can open up a webpage in Edge. lol
(Good thing is that you don't have to use it, nor should you.)
-Customization Options were made a lot worse than 7. Back in 7, it was pretty easy to make changes to the Default Profile and make changes across all created Accounts.
For some obtuse reason, they made this MUCH harder in 10. (This is mostly in regards to Network Accounts.)
There's some things you just can't apply to all Accounts period for no reason.
-Group Policies were also kinda borked for some reason. Like they removed/modified existing policies that were in 7 and worked fine, but decided not to put them in 10.
MS says you can recreate those policies, but I haven't really seen a way to do this yet.
-Forceful Updates: People have brought this up in other threads, but 10 really wants you to run updates.
So much so that if you refuse to apply updates a number of times, it'll forcefully restart your computer if you're in the middle of something.
You can avoid some of it if you modify some of the Update settings (like your "busy" hours), but it's gonna push those updates one way or another.
(This is kind of a good/bad thing; good in that updates do need to be applied, but bad in that it can potentially ruin something you're working on.)
-Dueling UIs; MS pulled this shit with 8 and it returns with 10.
There's your Settings UI from 7 which still remains, but then they added a second UI that is 10's, but the two styles are so different.
Sometimes they try to manage the same things, and other times, only one has what you're actually looking for.
Like they couldn't agree on which one to use, so they put both in. Pretty sloppy from my point of view.
Personally, I don't really care for 10. Optimized, it runs pretty well, but getting to that point is another story.
Frankly, it does a lot of pretty shitty stuff I don't really agree with. I can say it's better than the clusterfuck that 8 was. But I still prefer 7 for now.