Upgraded to a 6s from a 3-year-old iPhone 5, so my battery life wasn't great before, and I'm enjoying getting more time away from the plug.
Honestly, it's just awesome. I was so reluctant to switch because I thought I wouldn't be able to reach the upper part of the larger screen, but I've adapted, and now I can't remember how I ever lived with less screen real estate. I love the curved screen and rounded edges compared to my 5. Love the Touch ID. Even love the new vibration engine. Everything is SO fast. I'm glad I didn't know I would like it so much, or the wait to receive it would have been even more torturous!