Ive recently made the switch from 7+ to the S8 & TBH I'm really enjoying it. I've always had an iPhone since the original & was really worried about leaving the ecosystem but there are simple work arounds for most things - I have my calendar syncing with iCloud, Google Photos now handles my photos, music works great if you subscribe to Apple music (I don't so I'm using Amazon music instead of iTunes Match), I now use Whats app instead of iMessage (my friends aren't heavily in iMessage), Hangouts instead of Facetime . It was a bit of a faf getting everything working initially, but now I have it just as I like it & I'm really pleased I made the switch.
The S8 is a great phone, wireless charging is so convenient & the on screen keyboard has the numbers at the top (it's a revelation) - however the two things I miss are the awesome Touch ID on the 7+ & that when it's hooked up to my car stereo, it doesn't work in iPod mode with playlists etc being controlled from the head unit.
TL;DR Moving from a 7+ to S8 has been OK!