I (Moto X 2014) got a different set of bugs on M. Mostly problems with basic functionality:
- When I get called, half of the time I don't see the name of the person when they are in my address book.
- Music controls (which were already very basic) usually stopped working a certain amount of time after the last restart.
- Music randomly pauses when browsing the web at the same time (as in, I have to open up the music notification card and press 'Play' again).
- E-Mail notifications have been flaky for some reason.
- Active display music controls are worthless again. Google decided to add a 'favorite' button. Motorola just picks the first three buttons from the notification card. Now you can't go to the next track anymore.
Security updates were also still at the 1 November 2015 level. After being stuck for half a year on a buggy 5.0 release before getting 5.1, I know this is going to take months to fix, if ever (Lenovo probably doesn't care about the 2014 anymore).
I am now back to an iPhone after a Nexus 4, Moto X 2013, and Moto X 2014.
Now that you need to bring your own phone to most carriers, there is no reason not to stick with Nexus/pure Android. The updates work there for the most part.
Some genius at Google decided to make the phone vibrate and beep every time there is an open WiFi spot, or you need to sign up to a known one
Really
This kind of crap (not the only one) almost justifies the extra price for iOS