Got MM this morning, everything good so far. None of the issues discussed here, at least not as far as things that affect my regular use. I did not unmount and remove my SD card prior to the update, although I probably should have to be safe. I only keep music on there, but it's quite a bit. I use Rocket Player and it had no problems finding my music, so I didn't need to re-scan or anything.
One nice pro is it fixed a problem with text notifications I've had since the phone was new. I posted about it previously, that if I closed the screen from a text conversation, I did not get audio notifications from that person if they texted again. I had to be careful to close out that conversation before shutting the screen off, which was annoying if I was texting back and forth. A Sprint G4 user mentioned here that MM fixed that issue for him, and it has fixed it for me as well. I am getting all my text notifications no matter what screen I leave it on.
One potential con is I'm thinking my battery didn't perform quite as well today. I'm still not through a full 12 hours even, so more observation is needed, but I'm keeping an eye on it. I don't know anything about the Doze feature that's discussed here, I'll have to find out about that and see if something there can help me. I briefly went through to check on some of my normal settings that I disable to help battery life, ok google, gps, etc..little things like that. All my settings were retained, so I didn't immediately find anything that should hurt battery performance. But at this point, it might be all in my head. We'll see.
Painless so far.