So far so good with mine. I'm coming from an S5, so some of the upgrades are really nice:
Fingerprint scanner: Much better than the S5.
Smaller and lighter than the S5, especially if you had the wireless charging back on the S5
Seems to be faster than the S5.
Battery, in my hands, is about the same as the S5. Typically am getting 3-5 hours SOT. When idle, seems to use less than 2% per hour, and sometimes less than 1% per hour.
Lack of a memory expansion port hasn't affected me (I have the 64GB S6). I do have a micro USB cable that attaches to a USB drive if I want to do a hard backup of data.
I do wish it had a removable battery, but it isn't a deal breaker for me. I do have an external battery pack if needed in an emergency, but I don't see me using it much (if at all- I never used it with my S5). Odds are, I will replace this phone with another flagship phone in a year or so, so the battery longevity wont be an issue.