Marta's apartment was wonderful. The location cannot be beat! We walked to everything during our week in Barcelona. The flat has basics for cooking a delicious meal. There is a super market, a smaller local grocer, and a nice butcher/cheese shop just around the corner. We even loved the crazy shower - yes, you do pretty much have to step over the toilet to get into the shower, but the apartment has such charm and comfort that we were not bothered.
Two things to repeat that some have also said and should be emphasized - the flat is several flights up without a lift (about 100 steps) and the hot water heater in the bathroom is tiny. The steps were fine for us as we used the hike up to justify eating more delicious food. The shower worked for us by getting wet, turning off the water, soaping up, then rinsing. Otherwise, you will have to wait about 30 minutes in between each shower.
Overall, we would stay in Marta's flat again without hesitation.