Apartment very well located. Very clean. Well equipped. Easy to access (we used Aerobus from the airport to Plaça Catalunya, then a 15 minute walk). Great communication. Flawless check in. Greatly recommend.
4 people can sleep there (that was one of the reasons why we chose that apartment), but be aware that the more people you are...the more luggage you have, and with this narrow apartment this can be an issue if you are 4 adults, each one with 2 big suitcases and 1 hand luggage: you will find it hard to store them. (that was not our case : we were 2 adults with 2 teens, each one with 1 suitcase and 1 backpack, and I think this is the maximum this apartment can hold).
From time to time, during the night, it can be noisy: hey, you are near the Rambla! This is not an issue, but be aware that you won't be in a perfectly calm environment.
On the same street you have plenty of markets, bakeries, bars, an alcohol store with many whiskies and wines...the Boqueria, the Rambla...in fact, you are near from all you need!
The perfect place for a couple or a small family. I recommend that apartment!