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.