We loved our stay at Carlos's place! He was very helpful and accommodating, with great communication. We appreciated him letting us check in early, since our flight arrived in the morning. The apartment is snug (a little smaller than it looks in the pictures, as is often the case) but comfortable. Shower was hot with excellent water pressure! (Not always the case in Europe) There are lots of guidebooks, and some (US) plug converters, if you don't want to bring your own. The terrace is great, though we didn't use it a ton since it was winter.
The best part is the location, tucked on a quiet street in the Gothic Quarter, near a small plaza. Even though you're in a touristy area, you feel like you're away from the crowds. There are lots of shops and restaurants in close proximity, and you're a short walk from the cathedral, the Rambla, the Picasso museum, and more.