I will start this off by saying that the Galaxy S8+ is the best smart Phone I have owned, the last two being LGs (G4 and G5). In particular, the Snapdragon 835 chip really does cut power consumption. My phone easily lasts a full day. It is really responsive, and the screen is great.
But Samsung has absolutely terrible support.
There is a bad bug in the phone, and there is no way to report it to them. Phone support says "we do not support third-party apps." But multiple XMPP (Jabber) clients cannot connect to the popular Openfire XMPP server. This includes Xabber, Yaxim, Freelab Messenger, and IM Pro. And it is not just me alone. Several friends have the same problem with their S8, and there are multiple posts online.
Samsung does not answer their Twitter messages. T-Mobile does so instantly. The online chats only handle the most basic of issues. There is a Samsung app that lets their agents control your phone, but my agent did not have the Samsung end of it.
There are other issues too. I have the very nice Samsung case with a transparent front. Unfortunately, when you close it, apps such as GPS Tracker turn off. Samsung support knows nothing about their cases.
Then there is the very annoying volume warning that is mandated by the EU. But with my headphones, the volume must always be at its highest, and there should be a way to turn this off without rooting the phone.