We were very impressed with this apartment. The check-in is a little awkward as you have to go to their office first, and then to the apartment, so if you have luggage that's a bit challenging (and costs more to get the ride in between), but the process was pretty smooth. This flat is right in the middle of the city center, just a few blocks from Las Ramblas, two different Gaudi buildings, and a host of other sights and attractions. The promenade outside is full of restaurants and shops. Be advised, it is in the city, so it is NOT quiet. It could get quite noisy with people and cars and such going past, but that's what you get for being downtown.
As for the apartment itself, it was very clean - and maybe since it was last reviewed the policy has changed, but we found bath supplies, cleaning supplies in the kitchen, and a gift bag with additional toiletries and other stuff in each of the bathrooms - a very nice touch. The A/C worked great so that was a big help after a hot day walking around. The only real negative was the 2nd bathroom was a difficult configuration to use since the shower is not separate from the toilet or sink so everything gets a bit wet. But overall we were very happy and would stay again.