Maybe it was the weather, but the city itself is grey and felt a little grim, so unlike the warmth of Toulouse. Funnily enough, it was very like Toulouse in other ways. They were both important regional cities during the middle ages and, therefore, they were both centers of important events. There is a cathedral from about the same period and other big old churches. As in Toulouse, the Romans were there, of course, but their impact was not so evident. In Toulouse, one has the feeling that the Roman way of life was embraced and retained as far as possible after the fall of the Roman Empire. Not so in Rouen.
Where Toulouse had Cathars, Rouen had Jeanne d'Arc - who was imprisoned, tried, and burned at the stake there. Toulouse had the regional lawcourts, and so did Rouen. In Toulouse, they have been sort of replaced by modern buildings, but some important parts are incorporated very nicely into the modern buildings. In Rouen, they are still standing.
Unlike Toulouse, Rouen was captured and then colonized by the Vikings, who became the Normans. This may be one reason the Roman influence is less evident. The area went back and forth between England and France a lot of times. And then there was WWII. Toulouse was not damaged as much as it could have been. Rouen was badly damaged. A lot of important stuff, like the damage to the Cathedral and the Palais de Justice, has been wonderfully restored. While Rouen still has lots of wonderful old buildings, part of the city was destroyed and not rebuilt, so it lacks that feeling of being in a complete a old city, which is so wonderful in Toulouse. And of course, the style of architecture is quite different in effect.