We had a good time staying in Nicolas' apartment. His communication prior to booking and afterwards was excellent - really quick and informative. His father met us at the door to hand the keys over, explain the various bits about the apartment.
Unlike other places I've stayed, we did sign a little rental agreement (similar to AirBnB's terms and conditions) basically confirming price, name, passport number and the do's and don'ts. I quite liked this - although it was more formal than other places, it gives host and guest additional security with each other.
The apartment itself if ideal for a couple. You could fit another person in on the sofa bed (or a child, maybe), but it's a great space just for 2 :)
With a little supermarket directly opposite, another larger one just around the corner, there's plenty of food etc in staggering distance!
The walk to the Metro is around 3mins if you walk slowly, and Barcelona's system is really easy to get around. 15/20 minute light amble to the water front, less than that to La Rambla - meaning that the apartment is pretty much ideally situated for a quiet get-away.
The apartment is well appointed with a hob in the kitchen (no oven), decent sized bathroom (wetroom style) and a small outside terrace space. The aircon was a huge bonus and worked perfectly! The washing machine is in a cupboard in the outside terrace space and connected to the outside tap so make sure that you have turned the water on before you use the machine.
The neighbours are pretty quiet - we did hear some noise but not huge amounts and it didn't disturb us.
Overall, a nice space in a quiet corner of the city well suited to anyone wanting to get out and explore Barcelona!