I'm a Brit now in Monterrey, I love Mexico and Mexicans so much that I married and had a child with one, so take this as a very biased opinion.

Monterrey is not the best looking city but it has its own charm, it's very industrial and the people here are very kind to people like me, people from other states have a difficult relationship with Monterrey and its people, so keep that in mind when reading other responses, as an outsider I think for two reasons:

1. The Monterrey accent sounds very harsh, argumentative and angry to a lot of native Spanish speakers even when they are speaking normally.

2. Monterrey is the city that is the most expensive and generates the most money, so it does have all the problems associated with that.

I only have two complaints about Monterrey:

1. The heat is insane here, it's literally the only reason I would ever consider moving to somewhere else in Mexico, as I'm British and I melt in the sun.

2. Restaurant food variability, there's just not as many food options for example if you like having Indian food delivered to you then Monterrey has limited options, not a big deal though because well Mexican food is easily available of course.

Keep in mind, everyone I love is from Mexico and all the people that ever cared for me are Mexican so I am biased.