Lisbon is stunning. I am not a city break person, most of my favourite holidays have been in smaller towns. I love places like Verona, Veja De La Frontera and Valparaiso. I find them more managable.
Lisbon reminds me of these places, it's full of ocean views, orange trees and great seafood. Trams from the 1920's roll up and down hills between neat white buildings. It has one of the best art museums I've ever visited.
The food is outstanding. The first evening we ate at the Time Out branded market on the waterfront. It is outragous value if you don't mind being your own waiter. Also worth braving the queue is Cervejaria Ramiro, the seafood is fantastic.
It is a great city. If you are looking for a weekend european getaway I don't think you can do much better.