For my own future reference if nothing else, some quick thoughts on a few volumes of the Sfar/Trondheim DUNGEON series that I read recently, following enjoying the first I read, TWILIGHT v1 - DRAGON CEMETARY, which is later than these chronologically.
DUNGEON - ZENITH v1 - DUCK HEART is the best of them, and I gather the place where the story actually starts, in terms of order created. Herbert the Duck and Marvin the Dragon meet and start their adventures. A very imaginative and witty storyline.
DUNGEON - ZENITH v2 - THE BARBARIAN PRINCESS continues the story of Herbert and Marvin, but isn't quite as good. The first half involves an adventure inside the Dungeon rescuing a princess, with quite a few complications and twists. The second half has said princess joining them on a journey to get a new dragon to guard the Dungeon. A lot of high spots, but both stories drag between those.
DUNGEON - THE EARLY YEARS v1 - THE NIGHT SHIRT goes back in time, and adds Christophe Blain to the creators on the art. It stars the young man who would go on to be the Dungeon Keeper in the later books. Much like ZENITH v2, it has its moments, but overall it's the weakest of the for DUNGEON books I've read, really missing the Herbert and Marvin bits that make the others so enjoyable.
So, ranking the four in order
EARLY YEARS v1