10.
It had everything one could one. Room for expansion, a detailed settlement for the PC's to return to, evil plots, example of Goblin language, ambushes, secret doors, undead, a crazy hermit in the woods, evil cultists that had spread out, mosters that worked together and preyed upon one another.
It's one that the PC's can start in, and easily keep going with, eventually becoming the Castellans of the keep, clearing out the area, etc.
Plus, it had DMing tips, a rumor chart, and all kinds of things.
How many modules have you seen lately that have that much stuff. IIRC, it even had a player's map of the Keep.