Hello,
I just came back from a three day stay in AC Diplomatic with my wife and my ten year old daughter. I had chosen the hotel based on the rather favorable reviews I had found here. Unfortunately I am not able to confirm these reviews.
We arrived in the afternoon, where we were told the the room that was originally assigned to us was not yet ready. Instead we were moved to another room, which turned out to be a smokers room. Since we were tired from travelling we decided to take it hoping that some air would solve the problem of smoky smell. But when we came back to the room in the evening it was still smelly. The room was facing the street, so we had to close the window again, because it was simply too loud. But still then you could hear the street.
Next day I insisted on another room, quiet and non-smoker. It was a non-smoker room, but was unfortunately located right beside the housekeeping room. The housekeeping started to refill the cart with bottles and so on at 07:20 making such a noise that we had no chance to sleep any longer.
The interior of the rooms was o.k. (all wood, bathroom in marble), but this did not really compensate for lack of sleep (and sleeping well after an exciting day out is one of the foremost things I expect in a hotel).
Breakfast is charged separately at a silly rate of 18 EUR p.P, which amounted to what we would usually pay for a reasonable dinner elsewhere.
The location is fairly central, you can reach the place where the tourist buses start in about 10 minutes walk.
Given the comparatively high price (we booked superior) I feel that there are definitely better hotels with better value for money around around.
P.S: when I complained about the smokers room the manager on duty told me that I did not explicitly reserve a non-smoker (I thought this to be self-evident since I mentioned the age of my daughteron the reservation). So if you chose to stay there and prefer a non-smoking room you should make sure to note this on your reservation.

stayed march 22nd, although i read on this site that the air con did not work mine was fine. check in/out was fine. the only fault i could find was the breakfast buffet whilst it was o k i am used to staying in the american chains where they know what a buffet is, having said that this is spain so not to complain too much.

We stayed in the AC Diplomatic in 2004, but have only just found this site!
We found it a super hotel. My fiancé booked it direct over the phone and upgraded to a superior room. This meant we had an amazing balcony which wrapped two sides of the building and we could see so much of the city it was amazing. Unfortunately it was December so we didn't spend too long out there! The room was very clean, maybe a little on the small side but plenty big enough for what we needed. The cd player and free mini-bar were great, the marble bathroom was beautiful and the power-shower was really powerful.
The breakfasts were fantastic, with a huge choice of things set out as a buffet and other cooked options if you wanted.
The hotel is very close (easy walking distance - one block) to a metro station, some of the Gaudi buildings and some great bars and restaurants.
The staff were always very friendly and although we didn't get any response on the phone at 2am when we wanted to order champagne to celebrate our engagement, we went downstairs and the night porter swiftly sorted it out, with the bottle arriving less than two minutes after we had got back to our room.
Overall a super hotel which we would recommend to friends.

We stayed at this hotel between christmas and new year. The hotel is in a great location. The rooms are modern, and have a large bathroom. However, our room was very warm and the temperature control did not work.

The staff do not understand English. As we had to leave early in the morning, we asked if reception could have a bill ready and book a taxi for us. Next morning, it took four staff and 15 minutes to print our hotel bill. The taxi is a completely different story, but we end up walking !