Rouen is a beautiful town with rows of medieval half-timbered houses. It has a large impressive historic city centre and quite a few imposing Gothic churches headed by the famous Cathedral. The municipal court is also extensively decorated and resembles a Gothic church.

Rouen was damaged during WWII, so unfortunately, although impressive, it does not feature a unified urban ensemble. Therefore, it seems it cannot compete well with other French historic towns such as Colmar, Dijon, Sarlat and many more, let alone many such European towns. Nonetheless, large segments of the old town are well preserved and the quantity of the preserved portion still makes it one of the largest old towns in France. 

France in particular and Europe in general already feature so many historic towns on the list that it seems highly implausible Rouen should ever make it. Notwithstanding, it is a pleasant town worth visiting if you're around in Normandy.