Personally, I rather enjoy the first piece.
Not really happy with any of these, i might try a B/W one...
In both her body is very expressive, but her face isn't. In the first, give her fierce look and it's great. In the second, have her looking down in a regal way and it's great. Imo.
I like the first one. The white gaps look awkward. Her hair should fill the page. That may help you to make it flow from her head better.
The last one isn't Medusa ;-) But not quite the Octopus. He's only the Octopus in name, not a mutant or anything.
A nice piece though. Very strong and primal.
The first piece is well-done, and you can pretty much cut her out and place her on whatever background you need or want. You could fill some gaps with more hair, but I think filling the whole background with her hair would be too much hair.
The second piece desperately needs a proper background. Medusa herself is well-done.
The third piece is just wonderful. I don't know the character, but your piece teases him well and makes me wonder who this guy is.
I agree with Symson, I feel if you get that close to Medusa, the entire background would be hair. Its the star of the show