On deck 4 they are as wide as a regular balcony, but deeper. From deck 5 up they are slightly smaller in width but larger in depth. Also on deck 4 about 3/4 of the balcony is covered from overhead, but beginning on deck 5 and up it is mostly open. That means your balcony is exposed to the weather (sun, rain, snow???) and also occasional ash from the ships exhaust.
I have stayed in the aft balcony cabins. I would have to say I prefer the wrap around balcony's and deck 4 the best. Hope this helps.