we were very happy with the apartment. It had everything we needed. it took us about 20 minutes down to the beech/old town walking with 2 young children. it's a very steep hill on the way back though regular busses run close by.
parking is a bit confusing and we could only ever pay for up to 3 hours at a time though we found a useful app called elparking which lets you top up.
we'd definitely stay here again if visiting San Sebastian