Agree with the posters that noted that other brands are just catching up. Same questions have been asked about Aman, and the general consensus is just overall improvement in the industry.
I've only done a handful of Four Seasons--Jimbaran Bay, Chiang Mai, and Koh Samui. What I've noticed is when management has singled you out for better treatment then the service is phenomenal. And they are less stingy about upgrades than other brands. E.g. I was at the Samui property and was upgraded from a regular pool villa to a 3-bedroom residence. Total overkill, but much appreciated. Rationale was that a GM from another property put in a good word, and I had an amazing stay. But then shortly thereafter chinmoylad, my Virtuoso agent, had a weak stay.
In general I've found Four Seasons service to be solid and efficient, but not personalized in any way. At 2 of the 3 properties I've been to I just felt like a nameless guest. I know it's not Aman and people ask for room numbers, but there was a point where I joked I should just where a t-shirt with my room number on it to give my voice a bit of a rest. At the Chiang Mai property not only did everyone ask for room numbers, but during breakfast service they would tell you your table number when you sat down. So I had to remember table and room number and was asked multiple times during each meal.
I haven't made it to a Rosewood yet, but as MikefromTokyo points out above, sounds like they have promise. Would love to do the treehouse one outside of Luang Prabang!