Anantara is always good quality hotels, and the Anantara Riverside Resort in Bangkok is no exception from this. It is a great place. a little far out from City Centre, but the shuttle boat sails every ½ hour and is free of charge. 15 min. and you are at the Central Pier from where the Sky Train and the Express Boat can be taken.
The hotel is a small oasis with a nice, but very crowded pool area. The rooms are comfortable - we had a Junior Suite, but surely less will do. The breakfast buffet is enormeous, and again very crowded with people, but it functions well nevertheless.
There are several restaurant choices at the hotel - Traders Vic, Benihana and Brio (Italian) and The Market Place offer a nice evening buffet with Thai Dancing and entertainment while you eat.
However, pricing in the restaurant are certainly on the absolute high side! And vey often people seem to choose to go to the Centre for the dinner.
All in all a nice place for some days in Bangkok.

Enjoyable, clean and fresh on the river. Older rooms are nicely appointed and those overlooking the river with balcony are worth the time to ensure you get one.
Far enough from the smog of the city, but still only 20 minutes or so by shuttle into the heart of Bangkok.
If you are not doing business or into all-out shopping, this is a good choice for a Bangkok hotel.
The Pen is still my favourite if i am on business, but the Riverside is a really nice break.

My wife and I stayed at the Anantara on three separate occasions in October and November 2012. We had not stayed there before but went on the recommendation of friends who had been there when it was a Marriott. Our expectations were not disappointed as we found it a wonderful place to return from the bustle and heat of sightseeing in Bangkok. We could find no fault with the three rooms (one was an upgrade to a suite) as they were spacious and beautifully prepared. As other reviewers have commented there are a number of retaurants both in and just outside the resort to cater to the tastes and budgets of most travelers. We particularly liked the Numero Uno bakery, both for a delicious pastry filled breakfast or a light evening meal. Staff were friendly, efficient and always welcoming. The icing on the cake was the free river shuttle, a mere 15 minute trip to the city pier where one could transfer to other river transportation or the BTS (Skytrain) at Saphan Taksin Station. I cannot imagine a better hotel for the price in Bangkok!