First Hotel of Cosmos Tour. Out of way location from El Centro but easy Metro stop. Breakfast was okay, beds were comfy. Internet was free in the lobby, but they charge for it in the rooms.

I stayed at the Abba Madrid for 2 weeks during a recent business trip to Spain.
My overall impressions were very positive. The hotel is well located with a Metro station (Cartagena) just 50 metres from the front door. The Avenida de America Metro station is also close by.
Hotel rooms were fairly plain but reasonably spacious and comfortable and included a TV, minibar and a safe. Bathroom was above average with a good assortment of complimentary items plus a decent sized bathtub. The room service menu is quite limited though and delivery was not especially speedy. I found the restaurant menu also to be rather limited and only dined in once. Not a problem from my perspective though as there are plenty of restaurants within walking distance. Breakfast on the other hand was excellent - one of the best I've come across in a European hotel. Fresh fruit and juices and plenty of bakery items and hot and cold dishes to choose from.
All of the hotel staff I dealt with were friendly and helpful.
I found the best rate for the Abba Madrid through myhotelguru.com, a site I use often and highly recommend.
Overall I was very satisfied with the hotel and would certainly be happy to stay again on my next trip to Madrid.

Really convenient location, at the middle on way Madrid Expo to downtown. Situated near Metro station. Staff at lobby is freindly and multilingual. Large room w/ comfortable bed. But some regret because I can't found slippers & bathrobe in the room. It's strange for the 4 star's hotel.

I can't say enough about this place. Great clean rooms, nice bathroom and showers. The staff were helpful and friendly. The restaurant had a small menu but the food was great.

Location was a few miles from Plaza del Sol, about a $6-9 euro taxi fare, but the hotel was right next to the subway opening.