To me, very close to a 5 (masterpiece).
To note: I'm not judging this for it's mechanics such as the XP system or the monster design, thing I think as a DnD community we've learned can be done better, and how.
I am judging it as an intro level module which we can use to let people learn the game. I am also considering the characters, plot hooks and the player autonomy.
For the first two (out of four) sections/chapters of the module I think this is a clear 5. The intro is easy enough to understand, engaging yet with various ways it can be tackled - none which are "the obvious" way to do it. The enemies and the dungeon has notes in it to help the players learn skills checks, traps/check for traps, loot and roleplaying. This means that it also has all of that for the DM which is stellar to me. Kudos to whoever designed this.
The second section/chapter is highly open-ended which can be stifling to new players. This is made up for by not throwing all the various quests at the players, only one quest is basically mandatory to encounter, the rest comes only if the players explore, or after tackling the bandit quest. This lets exploration-heavy parties who tends to like the options choose which quest to prioritize and in this module you can do all quests, players aren't punished or forced to choose between one or another which is great for beginner level in my opinion (the players don't know this but that may or may not be a good thing, I don't know).
Potential Spoiler Below!!!!!
The third section/chapter is where I think that the combat encounters lose just a little bit of balance. While I believe that as a DM you can just adjust any encounters, there is one in particular that is not for lvl 3 players, especially in an enclosed space (keeping it vague on purpose). Even with the adjustment made for the encounter I think it's a party wipe waiting to happen if the players are new. There is also no alternative given in the module to fighting or chasing the big flying thing away which I think would be a good option. In the same area I think the place could be designed a bit less grindy but maybe that's just me.
I very much enjoyed the castle design.
For the final section/chapter I think it's a bit hard and forces the players to do it over multiple long rests which isn't inherently a bad thing. I do think the maps is unrealistic in size while the encounters themselves are interesting. The module also doesn't seem to assume you bring the dwarf from section/chapter 3 with you into the dungeon which I find odd to not even address as an option (the dwarf would also die to just about any trap).
That said I think I might be a bit harsh, I really like this adventure and look forward to running it, might adjust after that but I doubt it.