I don't find Headmaster to be particularly grindy, but I do feel like the developers have bit off more than they can chew with regards to number of characters, locations, even mechanics. Because of the lack of focus, players may not know exactly what they need to do in order to progress. It can be frustrating to go to a location, for example, the nurse's office, and see effectively a dead end because of missing/incomplete game content. These types of dead ends are very prevalent in Headmaster and probably make many players annoyed when they are trying to progress the game but find themselves having to check the 15 dead ends in game content in order to find the one correct path.
This is also a developer problem since, for example, it's extremely difficult to track the conditions and overall progress of the game. This update introduces the cafeteria, for example, but I immediately noticed a logic/programming error that allowed me to trigger certain events with the cafeteria when I shouldn't have been able to. Even in a very well architected game the complexity of the game's narrative and branching is not enviable.