Overall, the apartment itself is fine. It is in a location close to Sagrada Familia and easily accessible to both the bus and Metro lines. Barcelona is a very walkable city and we chose to stay away from the main tourist hotels to try to avoid evening street noise.
The check-in process was fine. There was a €40 check-in tax that was not mentioned in the ad or by the host until several days before check-in. The host was out of town and unable to check us in so had a friend do it. I asked him to show us around the apartment and show us how things worked but he did not seem to know himself.
The apartment is in good/clean condition. My wife and mother-in-law (who stayed with us) struggled with allergies throughout the stay due to the dusty/musty nature of the bedding. All of the towels and linens from the prior guest were left hanging on the lines off of the balcony. So, given that we needed to use the lines for some of our kids clothes that we cleaned, we took down all of the bedding and linens, folded them and left them for the host. As other reviewers have mentioned, we ran out of toilet paper in the apartment and had to go buy that.
The noise in the apartment building is my biggest concern. We arrived on 12/25 and had awful noise in the building on 12/25, 12/26, 12/27 and 12/28. This could be an anomaly because of the holiday but it was a rough few days. Fairly consistently on each of these evenings there was yelling in the hallways from 20:00-04:00. From 00:00-04:00, there was loud karaoke with 8-10 individuals drunkenly singing american hits from the 90s.
The electricity in the apartment is a bit iffy. If more than a few items are used on one circuit, it blows the main breaker. There was no rhyme or reason to this. Sometimes, the oven would blow it with nothing else turned on. Sometimes, it was the TV and the blow dryer. We were able to find the circuit breakers and reset it quickly, it just caused some issues throughout the stay.