I would say you will only be disappointed with the battery life if you came from an older iPad. The iPad 2, 4, and iPad Air all seemed to deliver better battery life than the Air 2.
I keep my brightness relatively low (35% or so):
Battery life with playing games and heavy video streaming I'll get about 10-12 hours usage.
When I just surf the web, email, Facebook, etc. I'd say about 12-14 hours usage.
Seeing 16-20 hours usage on the first Air was common. On the IPad 4 I used to hit over one full day in usage once in a while.