Abraham Lincoln: Vampire Hunter is a great joke. A brilliant one really. It trusts its audience enough to know that they - of their own free will - bought tickets to a movie called ABRAHAM LINCOLN: VAMPIRE HUNTER. So instead of obnoxiously winking at the audience, it plays it earnest (key difference from "serious"). Which is FUNNIER. For anyone who's seen Who Framed Roger Rabbit? (and if you haven't, stop reading and watch it now), you'll know that it never had an insipid character making "Hey, look at how funny it is that the normal people and the cartoons are IN THE SAME WORLD" comments toward the audience every 15 minutes. It expected the audience to be on board rather than transparently pointing out the obvious for a cheap gag. Ghostbusters had a similar attitude, as did Galaxy Quest - though those were comedies, the humor was character-based rather than trying to ridicule their own premise. Because again, that's funnier.
Abe Lincoln gets this, and it's rather refreshing.