The class idea seems all right enough. The Dracthyr are just a poorly designed race, however.
From a practical sense it makes no sense why Deathwing would want to create a race of dragon/humanoid hybrids when the larger the dragon the bigger the threat. Dragons have always been able to transform into humanoids, including himself, so he just gimped his own species into being physically and magically weaker as well as not being able to hide among the mortal races because of the scales still being present during transformations. All the downsides of being a humanoid in the WarCraft universe with none of the upsides of being a dragon.
Not to mention that the models look they came from a completely different game. They look nothing like WarCraft dragons and more like something from an eastern fantasy game like Final Fantasy. They're on the same level as the female Cataclysm model for the Worgen in terms of awkwardness. The designs are just bad.