I've stayed at the Siam a few times over the last couple of months. While it's hard to compare with "normal" Bangkok city hotels, this place is special and if I had to pick a single favourite hotel this would be it.

I appreciate good architecture, and this one of Bill Bensley's masterpieces. The property overall is stunning and has been filled with genuinely unique antiques and artefacts from the owner's personal holdings. Service here is focused around Butlers who are Aman-style rather than St Regis style and as well as being lovely go out of their way to make your stay perfect. As escape4 mentioned, other parts of the service in the restaurant or terrace are perhaps not quite up there with the best hotels in the world (and the cocktail menu really needs a revamp), but the Butler service does mean I'd say the Siam has the best service for me out of any hotel I've visited in Thailand.

I was lucky enough on my first visit to get upgraded to a Riverview Pool Villa which was gloriously beautiful, but having been in the "normal" Riverview Suites on subsequent visits I'd actually say in some ways they are the nicer room. On my last stay I had a private muay thai session with a former national champion and then a massage in the spa by someone who clearly knew a lot more about how to give a massage than even your typical 5* spa masseuse.

I'm usually running around the city on my days in Bangkok and so the hotel is a bit out of the way for me. While not terribly convenient, I still hope to be able to return every month or so for the time being (and perhaps once a year in the future) just to appreciate the piece of art it is.