From what I understand, Dresden suffered a 'perfect storm' on the night with the cloud opening up over the city as the bombers arrived. This allowed all the bombers to see and find the target, something that was not usually the case for most night raids and so the city took the full force of all the bombs.
I stayed in Dresden one night, right next to the cathedral. The re-building from the ruins is quite impressive, as was the support from around the world that helped fund it.