GOOD:
The location is great! You're basically a 15-20 minute walk from so much in the city and La Rambla is very fun and exciting. Also, the building seemed very safe — we never had any concerns about anything like that. The apartment size is pretty good for 2 people. Very clean. A little hard to find, but I'll admit that's probably because we didn't understand Spanish addresses.
NOT SO GOOD:
The noise. Even if you aren't a super light sleeper, it is NOISY. Very noisy. Basically impossible to sleep through the night without noise cancelling headphones. The mattresses are also not very comfortable. You can feel the metal springs after a while. The last negative was the building uses key cards to access each unit, but ours randomly got deactivated while we were out one day and we got locked out. It took someone 2 hours to bring us a new key, but luckily housekeeping was there to let us in earlier.
Overall, not a bad place to stay. Just be wary of the sleep situation.