We just returned from an 8-night stay in June, 2015, and loved it! Here are some quick pros, cons and tips for you:

Pros:
Oscar is wonderful, helpful, responsive. He gave us a great list of restaurants and markets; we were able to check out several of his suggestions and they were spot on. He helped me with random requests, like for a babysitter one night. We had a small plumbing problem that he had fixed ASAP.
The beds are so comfy and the shower pressure is AWESOME!
Plenty of room to accommodate all six of us.
Location - just two minute walk to Pl. Catalunya, which has trains/buses/cabs galore. There is a small grocery just a few doors down from the condo and a slightly better stocked one on the street behind the condo. You are also just a block away from Las Ramblas.
Cons/Tips:
These are more tips than cons. Have Oscar show you how to use the dishwasher and washer/dryer. They aren't like American appliances.
There are 15 steps before you get to the elevator. No big deal, but worth noting if you can't do steps. (There is a wheelchair lift at those stairs.)
We did have noisy neighbors for 2 nights of our stay, but we only heard them in the master.
The blue bedroom with the cute balcony is the warmest room and gets the most street noise (not much). If you're picking rooms and want cold and quiet, go for the gray room (with two twins). It looks the least cute online but my family called it the cozy cave.
My husband and I slept in the master; it had a sitting room to the side that was useful for suitcases and clutter.

The condo was very clean when we arrived and stocked with some basics like toilet paper and dishwashing liquid.

We also went to France and came back to Barcelona for one night and stayed in a well-rated hotel. Of all the places we stayed in Europe, Oscar's was our favorite by far. Clean, convenient, comfortable, great showers - and a wonderful host. We would gladly stay here again.