iOS8's continuity features with OSX Yosemite and now the Apple Watch. I'll be able to take calls, receive/send text messages on my Mac and it'll route through my iPhone.
https://www.apple.com/uk/ios/whats-new/continuity/
Nope.
Galaxy S2: 8.5mm, Galaxy S5: 8.1mm, iPhone 6: 6.9mm
If I'll be out without a wall socket for a while I'll just bring a powerbrick. Which is exactly what I did this Summer when I went to a 5-day festival in the middle of a field. I topped my phone up from 20% (from the previous day's usage) to 100% every morning and I still had enough juice in that brick to top up my GoPro batteries too.
If there's something truly wrong with the battery I can just book an appointment on Apple's site, walk into one of their stores and walk back out with a replacement.
iCloud is backup storage for your phone, and you get 5GB free, which is enough for a full backup for most people. It's there so that you don't lose messages/contacts/data if you lose your phone, and if you get a new one it'll just sync from that so you can pick up where you left off. Expandable storage would be nice though. There are cases/apps that do that now I think.