First of all, since i am going to list some minor flaws that could mislead the reader, let me state that i would come back to this hotel. That should clarify my opinion in first place.
I spent a week in october in this hotel, booked online a room in the 4 stars section. So far no extra or double charges but it was less than a week ago.
It seems actually made of 2 hotels, communicating through a plexiglass gallery. but all the staffing is handled from the 3 stars entrance, the 4 star reception and entrance do not work even to go out.
It's called art hotel i guess because is a themed hotel, but honestly and objectively the paintings are quite ugly. That does not affect the staying at all though and my compliments for facing the challenge to arrange such a theme.
The room is clean, not a surgery room but clean as you would expect it, a couple of signs on the wall did not make it less clean. It is cleaned every day, i asked within what time the rooms are usually cleaned up, been told never ever later than 3pm but in 2 occasions in which i came back from the city center earlier to take a nap, had to wait till 4-5ish for the cleaning staff to complete the job. yet considering how dirty amsterdam hotels usually are it was a nice and proficient wait. I spent those hours at the bar in the lobby, prices are affordable, an espresso goes by 2.25 euros, a coke around that. I didnt include a breakfast, i was happy with my coffee till reaching the center where there's plenty of cheap choices. Just be careful to the guy at the bar, just one of them, since it has a passion for keeping the change when it's too little, in his opinion, to give it to you.
One thing i really appreciated is the noise isolation, the room next to mine was populated with noisy guests but doors closed i could not hear them. The air system must be centralized and far from the minimum 21 degrees we are used to in canada, it could not be regulated so bring a good pijama to sleep. I carefully avoided to open the minibar since, as you should know, some people like to take beers from there and then refill the bottles with water to later argue they didnt drink anything, pretty common scam from hotel guests, therefore as in many hotels, opening the minibar triggers a charge automatically. There is a clear rules book in the room, take the time to read it. I asked if there was any smoking room in the hotel and been told no, but i found an ashtray in my room, that was as tempting as misleading. Not sure why though.
I appreciated the locker in the room, not sure if it's as safe as it looks like but when you carry a laptop and cash, it makes you feel safer.
As said, these are minor flaws and i would come back. True is not in the canal ring, but 10 minutes bus ride from central station and bus is every 15 minutes from 5 to midnight and every hour or so nightly. I would not trade that clean room with a central amsterdam hotel so i am happy with my choice and, if prices do not go up as a consequence of the heavy internet reputation campaign they are (honestly) running and if they keep charging by room rather than by person, i would definitely go back.