Just got back from Florence. Short review:

Room

The public spaces and rooms are lovely. I particularly liked the bar, which I thought was just beautiful, but the lobby, gardens, and rooms are all extremely nice. The gardens are absolutely huge (when you look on most maps of Florence the hotel is easy to find because the gardens constitute a whole "park"-like space on the map). Considering how little green space there is in Florence, it seems very extravagant, and definitely sets the Four Seasons apart from the other hotel options in the city. There were a couple of minor maintenance issues in the room (TV acting weird and a shower seal in need of tightening, but I chalk these up to working out the kinks immediately after opening).

Service

Service was excellent across the board. I didn't really notice any "new opening kinks". It's unclear how many people were actually staying at the hotel (when we went to the bar at night, we were almost always the only people there), whereas we'd see lots of people leaving the restaurant, most of them heading out of the hotel. Staff to guest ratios seemed very high, but this may have been because not that many people are staying at the hotel yet.

Dining

We only tried the restaurant for breakfast, which was very good. It was included with our rate, otherwise I probably wouldn't have paid 32 Euros for breakfast, but some people think it's a more important meal than I do. We probably should have tried the hotel restaurant for dinner instead of Enoteca Pinchiorri, which was a bit of a disappointment.

Spa

There is a spa, which is open. I didn't visit it personally, but will try to get a report on how it was. I don't know if it's intended to be the permanent spa, but it seems somewhat purpose-built.

Location

Location is less than ideal (this is the trade-off for the gardens). You're at least 10-15 minutes brisk walking from most of the sites than at more central hotels. The closest site is the Gallerie dell'Accademia, and it's probably more than 10 minutes away. There's very little in immediate nearby nightlife, restaurants or shopping. It's also off the beaten track enough that taxis don't seem to hang out in front of the hotel, which requires the hotel to call one for you, which means both a bit of a wait and a more expensive taxi fare (the taxis start the meter as soon as they receive the call, not when they pick you up). Having said all of this, Florence is a fairly compact city, so while the location isn't ideal it's certainly manageable.

Overall