+++ Excellent location on walking distance from all main sights, shops, bars, restaurants, clubs, ...
+++ Very clean
+++ Very well equipped (dishwasher, washing machine, tv, ...)
+++ Very good bed
+++ Quiet
+++ Nader is super available and helpful
+++ Pick-up service at airport upon request

One small minor: pretty dark (i guess the bright side of this is, it doesn't get too hot in the summer)

Conclusion: highly recommended for an urban stay in Madrid!

Thanks for everything, Nader!