OK, I can leave a critique
I took a look at this and I'll be straight, I gave it a zero. You say you want people to explain why they leave such low scores, and to be fair I'll give one.
The most noticeable things with this is the coloring. The coloring is rushed, spotty, and looks like a 5 year old did it with some cheap crayons. Even with low quality tools, a little more time and proper use of the tool can make it look much better.
In line with the coloring is the lack of shading and depth. The characters are very flat, you can really feel the two dimensions of the character when you should be striving to get the feeling of 3 dimensions. Also with the lack of shading and depth, the lack of a light source becomes painfully obvious.
Moving away from the coloring a bit and talk about a little more about perspective and anatomy.On Beetlejuice's snake body you see no tapering so you don't get a good feel of distance. The body comes to a short stubby end and seems like you just started randomly drawing a snake like body with little to no pre-planning. Similar problems are happening with the tongue. It has a varying thickness as it wraps around Lydia. On a plus side I am liking the face structure of Beetlejuice, it looks pretty solid
As For Lydia's anatomy, I'm liking the thighs, but thats about it. The breast are a bit too high and the mid section of her torso is a bit long. The feet could use some work and I think you need to practice some over all detail. Lydia's face I do not like at all, I think it could use a major tune up. The face lacks feeling of urgency in the expression and could use a lot of help looking like an actual face, cartoon styled or not. Clothing wise, the skirt looks pretty bad and I would suggest looking up some good solid reference and practice it some more. The blazer and shirt need to be more 3 dimensional and you need to get the body and clothing to compress under the binding of the tongue. This means you need to get some wrinkles in to the clothing and some indentations in the flesh where the tongue is applying pressure.
I think you should redraw this but put a lot more effort in to the thumbnails, rough sketches, line art, depth, shading and coloring for a much better final project.