Milan was probably my least favorite city in Italy. But I can’t quite put my finger on what made it so unattractive.
If you love shopping and/or fashion, I could see where it would have a draw. There are plenty of stores to spend away in, and it is known as being the fashion capital of Italy. But it doesn’t seem to have much else going for it. It is just another big city like any other big city in the world.
With one exception: the Milan Cathedral. The Duomo di Milano is gorgeous. It is intricate from top to bottom, and the church is massive. The duomo is a stunning building that is a definite must see if you are in Milan. But I wouldn’t say it is great enough to make a trip all the way to Milan.
It’s a pretty safe bet that you will end up in Milano at some point during a transition from one train to another anyway, so use your layover time to explore the city.