The space was very nicely decorated, clean, modern, and simple, but had all of the amenities that we needed. For 6 people, we all had privacy and space, so it was really perfect.
We all had mixed thoughts about the location, as the 'actual' positioning of the unit is fantastic - near all of the restaurants, bars, the beach, etc. We could walk almost everywhere, as San Sebastian is well known for. Our main gripe about the location is that it's on a major square, which is VERY noisy day and night. It's almost hard to describe it, but basically, on the weekend, we found it to be noisy until about 4am and then again from 7am onward. There's ALWAYS something happening there: bars, restaurants, marching bands (no joke), dozens of trucks trading goods, drunk kids, and on and on.
The noise was better when we closed all of the windows and blinds, but then the place got hot because we needed airflow. So basically, we loved the space and the location, but not the noise.
If you're young and going out late into the night, you might not notice this so much. Just something to think about if you're a lighter sleeper!! Otherwise, the Rentals Collection was professional, communicated well, and runs a solid business so I'd recommend staying with them.