Just got back from a stay at the Fairmont Orchid last month, which was our second or third time staying at the property, and loved it. The Mauna Lani is right next door (the properties are easily walkable from one another via the beach path) and felt very dated and sleepy to me, although I didn't see any of the rooms.
I think both properties are rated 4-star on hotels.com, etc. (with the Four Seasons being a "5") but from initial impressions, I'd put the public areas of the Mauna Lani at more like a 3 or 3.5...