I basically agree with you on the slang, and I don't see what the book would lose without most or all of it, except perhaps for a bit of jangly eyeball-kick cachet. The edition I had came with a handy glossary at the back, which I used quite a bit as I was starting out. But, yeah. I like dialect in literature, usually, but this wasn't even dialect.

My impulse would be to defend the content as being a bit more substantive than just male adolescent hijinks, but in thinking about that last chapter it seems to back up that reading--almost as if Burgess were saying Boys will be boys until they put away childish things and isn't that just the way of the world. I don't think that's what he intended to say, and I think the book has some interesting stuff going on, but I didn't get very much of the satirical edge that I think was intended.