Stayed here for 9 days in one of their Ocean View Prime rooms. We visited many other hotels on Maui over the 9 days (Hilton, Sheraton, ...) but we were very happy we didn't stay in those hotels.
We booked it through AMEX FHR (we generally get a good amount of benefits going through them so highly recommend doing that; but I should also mention that there are companies other than AMEX that have good packages for hotels in Hawaii).
The room was exactly what I expected so no surprises there; supposedly one of their best and I couldn't get an upgrade during check-in (they had only suites that were better than these and they were not available on the day we were checking in. The view was good. I like to have some garden/grounds between the room and the water to add some color (otherwise its just waves hitting the stones below and you could see that all day from any sea shore).
There is a huge garden on the 3rd floor. And floors above 3rd form a big U shape around the garden. We were on floor 6 and had a wonderful view. Well maintained colorful garden down and beyond that was the blue ocean.
There are tennis courts and basketball play areas in the 6th floor (floor that we stayed in)
Pools were clean and mostly empty on weekdays. Weekends were *very* crowded and noisy. Very kid friendly too - they had a kids pool with chairs around for parents to watch them.
No beach in Hawaii is 'private' -- but given the location and the kind of hotels nearby you generally have decent crowds on the beach. Not at all crowded or unpleasant. We spent many hours on the beach. There is a person there to help hotel guests with arranging chairs and umbrellas so you can just sit back and enjoy if you don't want to jump into the beach and enjoy the waters.
The whole area (Wailea) is a very pleasant place. Nice shopping areas, kids play areas, flowers and trees all around. Nice place to take a walk in the evenings.
Service: there are no complaints. We have read rave reviews about Four Seasons' service and attention to detail. Though I wouldn't give them 5/5 (may be 4.5?) on that aspect I still think it's the *best* you could get in a touristy place like Hawaii. We've had better experiences in hotels on the mainland (broadmoor, ritz carlton, ...). Reason I don't give them 5/5: we had to wait 1 hour before we could get the keys to the room after check-in (we just waited it out in the patio overlooking the pool while the room was being cleaned and setup). Otherwise everything else was upto our expectations for a hotel of this caliber: room was clean and tidy stocked with necessary amenities for ourselves and our 1 year old son (crib, baby wash items, toys, and such).
Tech: They do have free wi-fi -- but if you want to upload photos or watch a movie online it wont work. They have a paid ($20/day) connection that is more decent speed. They have a ethernet cable in the desk drawer so in case you dont want/cant use wifi you can still be connected. There is a iphone/ipod dock to charge your iDevice (not the new one, though, so iPhone 5 wont connect). Sufficient number of plug points (I saw atleast 8 points that were in easy to access locations).
The valet: these guys were great. Someone always comes and asks if we wanted a couple of water bottles for the day, wanted directions or needed beach towels or blankets (Halaekala mountain top reaches 35-40 degrees after sunset and we went there twice!). Every time we returned back to the hotel someone would definitely be there to help you unload. Very prompt, no-nonsense service over all. One of the best valet folks I've met. Whole crew was amazing.
Breakfast buffet: one of the best things about booking through AMEX FHR (that we regularly use) is the breakfast. It's free! The buffet is amazing.. they have a kitchen so you can order hot food or choose from one of the already cooked items - the standard stuff though.. nothing fancy/experimental.
Well, over all we had a fantastic time with our 1 year old. When our son grows a little older we *might* consider the "Grand Wailea" (right next to Four Seasons) - has a *lot* of water sports and kids specific social activities. Though Grand Wailea is more 'touristy' (it felt like we were walking on a giant cruise ship when we went there to check it out) we think it might be more fun for a kid.