Good:
i do not like the look of the 5/5s. I got the 4 in 2010 and the 4s in 2011 so thats 4 years on a squarish design. I wanted a change in the design language so I'm happy about the 6 in that respects
Bad:
to be honest I like the feel of the 4.0' inch screen more
i have medium sized hands and can reach across the screen on the 6, but to do so the phone would shift slightly on my hand. and the phone being as thin as it is with no hard edges, its actually really easy to drop. A case is highly recommended (I got a silicone apple case) even though I've not used a case on any other phone in my life.
I feel like the 4.7" screen is nice but the extra screen real estate isnt being used very well. I could do everything I could on the 6's screen on the 4s. if that makes sense.
The Ugly:
Durability. I don't drop my phones. At the same time, I don't really baby them, I chuck them in a bag pocket, in my jacket pocket. Sometimes with keys, coins, etc etc. As I said, I don't use cases but my iPhones 4S held up amazingly. Sure, there are scratches, but theyre only visible when theyre caught in a certain light. The iPhone 6 however, is aluminium, and theyre not nearly as durable. I already have a medium sized nick on the side, from who knows what. Thats when I decided on the case. I have none of that level of damage on the 3 year old caseless iPhone 4S.