I have had my S8+ for about a week, so still learning, but here are some thoughts.
The display is gorgeous and the phone feels great in my hand. I was surprised when my 5' 2" wife with smallish hands also preferred the 8+ to the 8. The retina scan works fine, but now that the newness has worn off, I think I will just use the simple 4 digit code which is easy to access. Along with many others, I find the placement of the fingerprint scanner to be a bother. I am also disappointed that while a few apps like the one from B of A will allow the fingerprint to sign in, they won't recognize the Iris Scanner.
My previous phone was a Note 4 and I keep feeling like getting the S8+ was a bit of "victim of advertising". The S8+ does everything it promises. I'm just not sure it does enough more to really justify paying $700 to replace the Note 4. That is probably more of a complement to the Note 4 than a criticism of the S8.
BTW, the hide it well, but the S8 does have S-Health, now labelled Samsung Health and still counts steps with a built in pedometer function.
The Smart Switch App was flawless. I transferred everything from my Note 4 using the included USB adapter while I transferred my wife's Note 2 using the wireless connection. Her's took 2 hours including 6 GB of Video and 16 GB of Music. Mine took about an hour with less music and video. It asks what you want to transfer and then just does it. I also backed my phone up to my laptop using the Windows version.
So, in conclusion, it is great phone, but older Samsungs are also great phones, so you may not see that much more functionality. On the other hand, the looks, feel and that screen may be enough to create phone lust and it certainly delivers on its promises.