If you're Horde, the main things you lose from gearing full Ret would be Gloves of the Hero, the Intellect Argas Ring, and Slipper of Unturned Loyalties. I use Serpent Gloves, Stillwater's, and Corpse Rompers in their place, and hit cap with drakewings + Lavishly jeweled ring.
That's all the BIS quest rewards you lose I think, because you can still get Both Int shields (Barrens one and Talrendis one)