While some MNG pieces can be so-so (think tissue thin tshirts much like Zara), I have really good experience with Mango.
I have ALOT of MNG dresses. Unlike Zara, they do a lot of formals - trousers, skirts, dresses, formal tops and blazers.
I have at least of one of these pieces. The quality is FAR superior to anything Zara makes. Some dresses are over 4-5 years old and still look amazing. I wear their cotton trousers a lot in summer and they wear very well.
I would say the sizing can be tricky. Tops are not always true to size.....sometimes they can be cut large. Read the sizes on website; those are generally accurate.
You can order a size smaller & your true size to compare.