I have to admit that I find answering the question “What is the Voynich Manuscript?” really hard. I suspect this is mainly because, in the absence of a ‘smoking gun’ proof, there are just about as many ideas of the Voynich Manuscript as there are people looking at it. Demonic, pagan, sexy, cool, meaningless, hoax, deception, written glossolalia, channelling, suicide manual, end-times warning, vowel-less Old Ukrainian, young da Vinci… the list goes on (and on).
Perhaps the most brutally candid answer would be that it is “a Scooby Doo mystery for grownups“: but I guess you knew that already. 😮
If you’re still struggling for your own answer, here’s an excellent article by Lev Grossman from Lingua Franca, way back in April 1999.