Most difficult would be the Vellum/Ink duo of books by Hal Duncan. Couple of books about three or four gay British/Irish guys who can step back and forth through time, alternate realities, etc. The concept is amusing, until the same scene is playing in five different eras of time and nobody's the same person. There's an apocalypse, angels and demons, a bunch of philosophy that makes little if any sense, a lot of mythology history (seriously, ask me about ancient Babylon. Do it.), and OH CHRIST I CAN'T GO ON, THIS SHIT'S BANANAS [sorry, had to]. I never finished Ink, but I've re-read Vellum about 20 times trying to get the point, if there even is one to discern.
Most boring... That's a hard one. Public education managed to sling a lot of them at me. Great Expectations comes to mind, man I really hated that book.