It's certainly his continually evolving backstory and acquisition of apprentices that has kept the sequels together, no doubt. In a way, 4+ balances out 1-3 in that 1-3's (particularly 1 & 2) structure needs to keep the audience in the dark over much of John's identity, history and motivations. 4-6 then lets us delve into that. But to what end? That's going to be the make or break here.