Ok get ready for a rant about 1st world problems.
It seems confused about sound. I had to uninstall Google Play completely so my official JBL OnePlus headset wouldn't start playing music in Google Play instead of Spotify.
These issues continued when I made my first audio recording. I was at the doctors and recorded the meeting, after that every time I try to play music from my headset it starts that audio recording. Even though the audio recording program is closed several reboots ago. Workaround is to open the phone, start spotify playing, pause, then I can use the headset as normal.
The worst bugs in a phone are bugs in the actual phone feature, imo. And in my case CM seems confused about the screen when I'm in a conversation. It's supposed to darken when I move the screen to my ear but it never lights up again when I move the phone away from my ear. Often I have to unlock the phone to end a call. The headset also seems unable to end calls, only answer them.
Waking up it's very sluggish, sometimes unresponsive. It has this "knock knock" feature where it wakes up if you tap the screen twice. This feature worked for a day or two when it was new, then stopped working for several weeks until I tried installing a stock android image on it and failed, reverted to CM and then the knock-knock worked again.
Even though the knocking works to wake it up, it often will not accept input for those first few taps after it wakes up so you end up having to erase your unlock code and start over a lot.
And speaking of stock android. Since none of my friends with stock android phones, nor me with my Nexus 7 at home, seemed to suffer these issues I decided to try the official stock android images from OnePlus.
I ended up in a reboot loop issue that has been reported on the bug tracker and on the forums. The problem is that I can't have my sim lock on if I want to install the android image because then it keeps rebooting the phone as soon as I unlock it. So I had to revert back to CM because I didn't feel like disabling the sim lock was a good option.
I could probably go on if you give me some time to think about it, there are definitely more bugs that I have experienced in my short time with this phone.
On a personal note, I was intrigued by CM because I am a FOSS junkie and know that it's a fork of android. I've had phones like the N900, ZTE Firefox OS and Jolla in the past. I love ideas like Replicant. So you understand why I bought the OnePlus. But in retrospect I should have just gotten an Xperia or an HTC since they have both provided models with unlocked boot loaders and Sony have even opened up their Android source code.