Dragonborn, yeah. But Dawnguard? Compared to Shivering Isles or Tribunal or Bloodmoon that might as well have been nothing at all.
Dawnguard does not add some nice new landmass to the map but it is still quite large. Two huge off-the-map areas, a pretty long questline, the best companion character in the game, lots of little new things, a dwarven sidequest, etc. I'm not sure how it measures up necessarily (Tribunal was pretty dinky compared to Bloodmoon as well) but I got my money's worth out of it.