Stayed long-term at Marta's apartment, from January to end of February and had an amazing time there. Would even return in March for an extra week but I had to cancel because of a family emergency.
I've met Marta and she is super nice, flexible and answer all communications fast.
The apartment is pretty much what is on the pictures and descriptions. It is a very comfortable apartment with everything you would need: nice beds, shower, and kitchen. The living room is also comfy although I used it very little. I stayed 2 months in Barcelona and can say that the apartment's location is one of the best you could get! Very close to two metro lines and three buses lines. In less then a block from the apartment you have places for a coffee, ice creams, markets, pharmacy, and restaurants (ramen-ya and can kenji are AMAZING options for ramen and japanese food). Besides that, Gracia is one of the best neighborhoods in the city, with plenty of restaurants, bars and nightlife.
Another positive aspect of the apartment is that it's located on the back of the building, with views to the inside block, which is great, making it very silent, something difficult to find in Gracia/Eixample area.
In summary, Marta's place is a great option in the Gracia/Eixample/Sagrada Familia area, I absolutely recommend it. You will not go wrong!