It's truly worthy of respect how Mike Mignola single-handedly built a comics universe off of his own back with nothing more than a handful of characters, some sharp writing, and some of the most gorgeous art ever to emerge from the comic book industry.
This splash page's importance can be explained succinctly. Mignola was never a fan (at least early in his career) of big, gaudy splash pages, preferring to stay neatly in his 3-6 panel pages whenever possible; the beauty of such striking Mignola pieces such as this are always as visually pleasing as they are rare.