The QM2 features several types of balcony staterooms in the Britannia category, including some that are known as "sheltered" because they are set back in the hull and thus provide some protection from the elements, which is nice on crossings because even in peak summer months, the weather is often cool, breezy and wet. These balconies also offer more privacy and cost less than glass-walled balconies. The downside, of course, is the view from a seated position.
Sheltered balconies are located on decks 4, 5 and 6; deck 5 is preferred, as it is sandwiched between stateroom decks above and below, so there's no chance of noise bleed from a public room.
Here's what a sheltered balcony looks like from inside the stateroom:
Here's the view when seated (it was a gray day):