I regularly come to Harvester, mostly when I'm alone during the weekend , as it is close to my place, with decent food, buffet style, possibility to add some extra dishes (I love their fried carrot-noddles), reasonable price and last but not least quiet atmosphere (at least in the room behind, i.e. with no TV). Then I also agree that depending on the day/time, the choice of dishes may or may not suit you, that the staff could smile a bit more and the room be refurbished. In the same buffet-style, with same owner, I largely prefer Bijas at HKU (5 stars) which is also cheaper (as it benefits from the university subsidy). 4 stars for this one is a good rating. I also understand those who give less.
Cons: limited choice (depending on time), old room that would need to be refurnished