Sure the gameplay is well tested (it has a overwhelmingly positive on Steam already from Early Access), but it’s a huge game, and everything beyond Act 1 is brand new, plus many things in Act 1 have been changed (ex. one origin character was rescripted and recorded).

So while the gameplay and the implementation of the 5e ruleset is well known, the rest of the story and the journey is still mostly new, and that’s a huge part of what will make people enjoy the game or not.

Just my few cents on why it’s still important to see how it reviews. Mortismal Gaming is already reporting that there are some crashes, bugs in the release version, especially in the later acts (even if that is normal for a game of this scope, it’s good to know).