I had done some prior reading (like a good Android purest does) and new that the update created some lag, but overall it seemed like no big deal. My Nexus had already been dealing with occasional lag, but being a 2 year old tablet that's expected.
The moment I got to play with the update I immediately regretted it. Everything lags. Everything crashes.
After a week and plenty of reviews, it's pretty obvious that Google should probably have made the decision to to exclude the Nexus 7 (2012). I haven't read a single happy review. I've found minor solutions, but they're all temporary fixes that don't really help in the long run.
I said this isn't a review because I don't think what Lollipop has done to my tablet is a fair assessment of the update. I imagine on a newer device it will fair much better. On my Nexus it's nothing but frustrating.
I'm always against rooting my devices because there's always a chance of bricking it if not done right (sometimes even if). In this case, I'm so frustrated with my updated tablet that I keep considering rooting it to remove the update because with the update it's as good as bricked anyway.
I will say, if you're a gamer, not all is entirely lost. While initializing a game may take some time and lag a little, once you get started games run great. This is good news for the husband who's tablet use is probably 75% gaming. Mine is probably more like 15%.