>>227671
Mechanically, it's a stripped down D&D- ascending armor class, old school-styled saving throws, standard ability scores, and the like. Nothing special but that's alright, because it's not selling itself for it's shiny, innovative mechanics.
In my opinion, where it shines is the kind of story it's geared towards telling. For example, take a normal, level 1 adventurer in D&D.
BTW is geared towards telling the story of how that level 1 adventurer got started, if that makes sense. The whole idea is centered around you being fresh, untested (whereas a normal D&D character might have had years of practice and experience beforehand just to be level 1), and inexperienced.
But my favorite thing about it is the playbooks, and I'll upload an example. You roll your background on a series of tables, each of which asks a different question, and your roll answers it. This will up different stats (Sort of like M&B character creation), and give you different skills or goodies. It also helps craft a really neat story for your character if you're stumped/lazy.
These playbooks also affect other characters- there's a table where you did something, and the friend to your right was there with you. If you get +2 con, he gets +1, and things like that. It helps forge inter-PC relationships if your players aren't used to thinking about those, or are totally new to RPGs. It helps you, as a DM set up a more personal home for these characters, because you start to think about who these NPCs are in relation to your characters, because these are people the party grew up with, worked with, partied with.