Amsterdam is definitely bottom of the pile.
To be fair to Milan, we went in November when it was lashing down with rain, and stayed a bit too far out of the centre (only our 3rd city break when we weren't as good at research and planning). The Piazza Del Duomo and the Duomo itself was the clear highlight. 2nd best was the Starbucks roastery that had recently opened - a bit like Charlie & The Chocolate factory for coffee lovers! Apart from that, meh, can't see what all the fuss was about.
There are no really any other cities that disappointed on the level of those two, so I guess it's a clear bottom two.