A lot of reviews allready covered most of the positive and some cons. I will point out the most important questions which may have left unanswered
1) Yes you can play Youtube . There is a placeholder bookmark when you first setup the device and it will direct to silk or Firefox browser which directly links to YouTube. 2) Yes Amazon Prime works including UHD(4K) content 3) Yes Popcorn time / Mopehus TV is easy install and works really well
NOTE: If brightness on your TV looks weird or off that's cause firestick has HDR on by default. Go to settings - Display & Sounds - Display -Dynamic Range Settings and change it so adaptive and it will fix the issue.
Cons/Bugs - Atleast on my tv ( Hisense) if you use voice commands to switch off and switch on right away the next time those functions don't work and you manually have to use the remote - Firestick app is awesome to control tv but the app keyboard has issues. Some letters like "s" and "r" donot register .