Installed 10 earlier today, and apart from a small glitch with recents that was fixed with a second restart, it's working perfectly. All of my settings are the same, all notifications are working properly, calls and texts are working perfectly... overall not a single issue. I'm actually a little shocked :O Honestly I fully expected to have to do a factory reset to get my phone working properly again. And dark mode has to be seen to be believed, it's amazing!!! The overall look of 10 is much more polished and stylish than 9.... easily the best looking Android os Google has ever put out. And there's some very nice features that have been added in as well, more than I can name here.
I'm running a first gen pixel, and the download and install was quicker than a monthly security update.... not sure why, because it's almost a gig in size. It only paused once, which it does for me every month when installing the monthly update. Just remember to restart twice.... three times if you want to be safe.... and everything should be absolutely fine ;-)