In Vance's picaresque tales, the villain, to the extent that there is one, is not integral to the tale: the real villain is the protagonist himself, who is usually not the winsome rogue the word "picaresque" sometimes evokes but rather a blowhard, a semi-competent or incompetent egotist with few or no morals; such protagonists--for his picaresque tales are all meant as savage humor--ultimately prevail (if they do indeed prevail) either by blind luck or by dint of their lying and cheating ways. To my own tastes, Vance's picaresque tales are his least successful (though still books by quality), owing to the protagonist's often failing the test I set out elsewhere on this site: "we can have no understandings with folk whose mental processes, intellectual or moral, are simply alien to us"--we cannot fathom them, we cannot empathize with them, we cannot enjoy them, save as we "enjoy" seeing someone slip on a banana peel. For myself, Vance's two "Cugel the Clever" novels are his least satisfactory mature work; but his novel Showboat World (the publisher's title--see the book list below) is much more enjoyable, perhaps because the protagonist, while another blowhard, at least has some scraps of wit and ethics and courage.
http://greatsfandf.com/AUTHORS/JackVance.php

I liked the Cugel stories best of all and have read everything Vance ever wrote. I find his "likable" heros (what the hell is the plural of hero...?) kind of boring. I find it a weakness in his writing that excepting his picaresque tales, all his protagonists are basically the exact same boring person with different names slapped on.

Although Cugel is a rogue... it touches on something in me... the idea of getting down into the dirt of life, really playing The Game. To actually find a way to identify with most of what life is, all the wisdomless striving, the backstabbing and so on; as opposed to mostly standing aside of it all and only acting to defend one's self from these endless rogues.

Earlier the person who wrote the above said though said:
A final thought on character: we must have for a protagonist at least one of two things--liking or respect. We can have both, but if we have neither the book means trees killed for naught. (Note that the lack of a quality does not necessarily imply the presence of its opposite: we may lack liking for persons without thereby needing to dislike them.)

(Based on some conversations since the paragraph above was written I think I had best point out that "respect" is a morally neutral term--it does not necessarily convey positive qualities, as we may well have respect for a rattlesnake owing to the danger it embodies; "respect" as I use it above signifies an appreciation of magnitude in a character, whatever that character's nature. Many great protagonists--in several senses of the word "great"--have been folk we would not by choice invite to our next dinner party.)
http://greatsfandf.com/apologia-1.php

Any dangerous human is worthy of "respect" I would think... Would 'interesting' be a better word?

Too general.

What is it about Cugel that makes him OK? I don't know exactly. Maybe just that it's funny while still being serious and dark. Funny in the sense of laughing at his stupidity. What better thing to laugh at then an evil person.

Yet at the same time he is sort of likable. He has such a positive attitude...

I have no idea really. I haven't been thinking very well lately. Probably because I've been relatively happy the last few weeks.