As for me, I like this graffiti. Not for its a bit scary and dark image, but for the sense which passed by through it . I think this graffiti tells about the censure of the creators of graffiti, about the prohibition for them to create. Thus,  through the image of snakes the author reflected the image of people who are against graffiti.

Wikipedia says: "Graffiti (singular: graffito; the plural is used as a mass noun) is writing or drawings scribbled, scratched, or sprayed illicitly on a wall or other surface in a public place. Stickers and other adhesives are not considered graffiti. Graffiti ranges from simple written words to elaborate wall paintings, and has existed since ancient times, with examples dating back to Ancient Greece and the Roman Empire". Well, it could be very interesting to show ancient Greeks something like that and notice their reaction...

I dislike this graffiti. I think that there are negative emotions coming from it. This picture resembles a nightmare. To my mind this is kind of vandalism.

I don't agree with your point of view! I don't think it's vandalism. I prefer this wall to clear one. It doesn't matter what emotions it сontains. It's very beautiful. That's important. Vandalism is when people paint some obscene words and scribbles.