So far, so good. Haven't noticed any lag yet. The phone did get pretty warm during the update but from what others have been reporting, that seems to be normal.
It did take me a while to figure out how to get Smart Lock re-enabled so I could add my Pebble as a trusted device. I can't say I'm a huge fan of the permanent Google search bar, though. I do like the new notification pull down layout and the built-in flashlight. I went ahead and kept the Moto active display notifications and haven't tried out the Lollipop lockscreen notifications.