Battery drains a lot faster compared to 10.0.1.

GF's SE updated to to 10.0.2 the day after it came out. No change in battery life stats, according to her. Updated via OTA. There's the issue (a known bug) with some of the new iMessage apps/games refusing to load until she exits Messages and swipes it away in the task switcher before relaunching it, but in terms of battery drain and smoothness, it performs like a champ.

One thing I've realized over the last couple of years is to never mix update sources. Either go OTA all the way or iTunes all the way. Never update to one version via OTA, and then the next version with iTunes, etc etc - in my experience, that's what caused all sorts of issues for me. I've not had any major issues (touchwood) with my 6 from iOS 8.2 all the way to 10.0.2 after I ditched iTunes and went OTA only. YMMV, but that's been my experience.