UE4 is one of the most powerful engines available, and is free to use. What makes this one unique that justifies the subscription?

I read the 1st review and it sounds like there's no reason to bother downloading this because it isn't useable unless you subscribe or buy a premium update or something. Would a responsible party please fill me in. I guess I could just go ahead and download it but I'd like to know if it's worth my time or not. Thank you...

I keep hitting launch, then for one second it says running, then nothing, it just doesn't launch, help!?!?!??!?!?!?

Questions for the devs: I see hints of Linux support at SteamDB - is this engine adding Linux support, then? If yes, then I'm curious as to what spurred that decision? Are there any games available on Steam which use this engine? Will they be released for Linux? Thanks in advance!...

i got this and i ran it as a demo however, i have no idea how this kind of software works ,could someone just point me in the direction of how to use it properly or can someone tell me if im wasting my tiem either is ok