Joes's Bar by Munoz and Sampayo impressed me with it's bleakness. And of course the expressiveness of Munoz' drawings. The Alec Sinner albums are also great.
What was the first graphic novel is a debate still going on, but for what was the first important graphic novel, the answer is clearly Maus. Together with Epileptic and Jimmy Corrigan, it's the holy trinity of graphic novels, showing the way it can be done. I've never cried from reading a comic, but must confess I came pretty close reaching that last page of Vladek and Anja finally meeting again.
I'm not sure how well the historical saga Passengers of the Wind has aged, but I enjoyed the five album series when it first came out. Well drawn and impressivly researched, but Bourgeon, the old fox, was careful to also include some nudity in each album.