The blurb on the back cover of Boulevard is by Art Spiegelman, who writes, "At last the general public will be allowed to discover Kim Deitch, one of the best-kept secrets in comics for over thirty-five years." Published by Pantheon in 2002 (and Pantheon is still probably the mainstream publisher most committed to graphic novels), Boulevard, it seems to me, is unlikely to really appeal to the "general public," even with the support of Spiegelman. Deitch's drawings often seem incredibly busy (sometimes virtually every surface is marked out by obsessively diagonal shading lines), sometimes to the point of hallucinatory confusion.
Yet, here, of course, that busy-ness and confusion is a reflection of the content of the narrative, and supports it, rather than simply annoying us. Still, the plot of Boulevard is itself nothing simple, following the fortunes of an animator/comics creator and his imaginary (or hallucinated) feline muse/alter ego/personal demon Waldo through much of the twentieth century (though not presented chronologically, either). Waldo, a cantankerous jerk, is a dark version of a trickster cartoon cat, whose shenanigans send one character to the asylum and another to life as a homeless bum.
For me at least, I had difficulty with the under-examined differences between comics are animated cartoons in the narrative. Clearly, there is something meta-fictional going on here, probably at more than one level, but Waldo's life within the creations of the main characters (as opposed to in their real world) is almost entirely in animated cartoons, with only a tiny excursion into comics, which makes the meta-fictional level either more complicated than I could follow or simply reliant on a too-easy equation between the two forms. Even so, Boulevard attempts an interesting vision of cartooning history, including an alternate origin story for Disneyland, another character based on Winsor McCay (called "Winsor Newton" so also riffing on the name of an ink and paint manufacturer, Windsor & Newton), and other various in-jokes: these, too, may ultimately be a barrier for members of the "general public."
I first ran across reference to this work in Jared Gardner's "Archives, Collectors, and the New Media Work of Comics" MFS Modern Fiction Studies - Volume 52, Number 4, Winter 2006, pp. 787-806, and Gardner does have some interesting things to say about Deitch's work, so do track down that essay, if you're inclined.