I had my hopes up, thinking the S6 would retain some of the great things that helped create and maintain the Galaxy line/brand. But, no SD card and a non-removable battery are both deal breakers for me. I get it that some people don't care and it's all good. My wife and I both have G3's and we frequently travel. A spare battery has came in handy on more than one occasion. I don't care about quick charging. I can go from 5% to 100% in less than a minute. We also have a young child and take lots of pictures. Large capacity SD cards are cheap. Much cheaper than $100 for every 32gb or 64gb increment. I also like putting the SD card in an adapter, plugging it in to my laptop/working with the files easily while not having to be tethered to my phone the entire time. They're also good for backups from time to time. If they think non-removable storage is better for the consumer, why are digital cameras not manufactured with it? IMO, it's not better. More phones are sold and the profit made using internal storage is crazy. It sure has treated Apple pretty good. Lastly, and this is just cosmetic, I can't recall a time that I thought about my phone and wished the back was glass. Sure, I keep a case on it...no one would ever know the difference. That 'premium feel' is determined by the case being used. As far as being practical, well, a glass back and practical probably shouldn't be used in the same sentence outside of this context.
I like Samsung and will probably go with the Note 4 soon due to my perception of the S6's shortcomings. If the Note 5 and/or 6 go the route of the S6 and no other huge innovations come around, guess it'll be time for me to jump ship.
I totally understand people liking the S6. It looks good and has some great features. I'm sure it'll make a lot of people happy.