From what I've heard, Android 5.0 on the 2013 version of the Nexus 7 is incredible, as long as your device avoids most of the issues from Lollipop. The issues are rare, but some of them haven't been fixed yet. Otherwise, the tablet seems to run great when everything is running properly, and Lollipop brings some nice performance and battery life boosts!
My Nexus 7 is running Lollipop. It's great, and it doesn't drain my battery. However, I still can't connect my tablet to my computer. The touch issue is still not fixed. Still, overall, the Lollipop is a great update. I hope that Google doesn't stop supporting this model anytime soon.
I've installed Lollipop, but switched back to 4.4.4, because at that time root wasn't available for Lollipop, tablet was running slower, had some problems with .webm formats, normal Gallery was removed and had to connect my Google+ account with it.
It's actually a great update for me. It seems my device is working faster with the new update. Just the same thing with se7en, it sucks that the normal Gallery was lost and I have to connect my Google+ account with it.