So I did the OTA a couple days ago and haven't played with it too much, since I prefer to arrive at things organically; discoveries in day to day usage.
So far I guess I have mixed feelings. The new material design theme looks pretty cool, I had a similar theme on go launcher or something a couple years ago. So it's cool that google caught up to that, albeit years later.
Animations are neat and it gives the OS a perceived smoothness to it, but do they really have to be everywhere? I suppose so. Not so much a complaint as an observation, but things do seem just a tad slower in real time, so considering turning them off, but like I said they are neat and aesthetically pleasing IMO so I'll keep em around.
The chrome tabs being changed to recent apps is terrible though and that was turned off immediately. Another negative is the pics, screenshots and downloads being put into photos instead of having a gallery like before. Although I suppose this is, like most things in lollipop, a matter of just getting used to it. As mentioned above, a gallery app can be installed.
Battery seems a bit better, although this could easily be placebo so not putting much stock into that. The new way of battery percentage being displayed is also a regression in my view. A "percentage of a percentage" made more sense to properly asses what's really going on, and personally came in handy a bunch of times.
The new keyboard is interesting, haven't really noticed an increase in performance here, autocorrect is spot on but I had no issues before.
My phone goes into landscape mode unprovoked a couple times a day, that's not cool. But livable-with. The silence mode has to be a bug, just has to. I suppose my biggest gripe is that a couple things take a few extra steps now, I don't really wanna have to swipe twice down to access settings. Or swipe down from the lockscreen to get full controls for Spotify, etc. White backgrounds are fine, but if this was amoled I'd be terrified of screen burn in like I suffered with ALL my previous samsungs. So that's probably the biggest reason I won't upgrade anytime soon. I like this screen quality and size, so I'm pretty set. Plus being a nexus I'm glad we have lollipop and hopefully the next update as well.