We stayed 3 nights at Hotel Unico a couple of weeks ago. For me, the location is the best thing - surrounded by great restaurants and bars and easy to get around Madrid. We had a garden room which was smaller than I was expecting - and we did hear our neighbours closing the wardrobe doors and moving the bed on a couple of mornings (esp. the ones above us) which was a bit annoying.
I sort of agree with some of the earlier comments around 5-star boutique hotels. The check-in was slick and everything you expect, but the check-out was rather clumsy and felt rather rushed. I would have liked someone to ask how we had found our stay.The concierge chap at the front of the hotel was super friendly.