Well, we visited, and it was reasonably sunny. First the good: it is undeniably beautiful, the stained glass is magnificent. But there’s a but. It is small and crowded. Besides the glass there isn’t much else to see. This wouldn’t matter much if you didn’t have to stand in line for at least half an hour and didn’t had to pay a 7,5€ entry fee, which is just too much to stare at glass (even if it is stunning) for 20 minutes.
If you only get one chance to see stained glass in European churches, this is the best pick. For the other folks: see a concert. As a stand-alone visit it wasn’t living up to its cost for me.