It's an odd hotel, and relies far too heavily on its reputation: many Amsterdammers still seem to believe it is the best hotel in Amsterdam.
In reality: the restaurants are good but pricey, and the rooms are variable. The premium rooms (across the alleyway) are lovely, the main block rooms passable, with some particularly pokey single beds ones. It's a sprawling old hotel, so the queue to the lifts for some of the outlying wings can be quite large if there's a conference in!
I've stayed in one of the apartments Aviatrix described - there's a couple of good ones on that block, and a couple of appalling ones. Worse still are the apartments that you access via the passageway used for kitchen deliveries!
It wouldn't be my first choice, but I wouldn't complain at all about staying there on a good rate. Its location could hardly be better.
One word of warning, though: unless things have changed in the last two years, do not get a taxi either from the concierge/doorman, or from the rank in front of the hotel. This used to be basically mafia-run (I knew several drivers who wouldn't even drop you off directly in front of the hotel), and you were asking for trouble. Call TCA yourself or go to the rank outside the Albert Heijn on Nieuwezijds.