As anxious as we all might be, I probably wouldn't be the first one to do this upgrade. I'd wait a few days, maybe even a week, before installing this. Past experience tells me that some important functionality will be either lost or changed. Let other people serve as the guinea pigs, and then we can all make an informed choice.
Now, if you really wanted to get anal about upgrading, you could make sure all your "mission critical" apps had been updated for, and are compatible with Lollipop. The major problem with any Android update is that once you jump in, you can't go back. So, if everything works well and you're happy, you pat yourself on the back. But, if something goes awry, you'll be kicking yourself in the arse until handset upgrade time.
I jumped in and got the update. Downloaded and installed with no hiccups. Everything is running smoothly so far. I won't go into too many specifics about my device but I run Nova launcher and many of the social media apps. I sucessfully sent and received a text message and I am getting notifications for other apps. The animations are smooth and I don't see any lag. I personally like the material design. It is a much brighter interface than what Samsung did with KitKat. I'm sure I'll find more new things as time goes but I did find the Smart Lock feature and that is great for turning on a screen lock while out and about but trusting my home so it turns off the screen lock (PIN). I am happy to answer any questions about my experience. Good luck with the update.