Some copies of the book have a dictionary at the end if you ever have trouble with a word. You're going to have less trouble reading if you speak Russian, or memorized every Nadsat word.
http://soomka.com/nadsat.html
Anthony Burgess did a wonderful job in writing it, and an even better job in screwing with our minds by writing a gibberish language that requires some amount of intelligence. I love that man.
Back on topic, making up words when writing a book isn't always a bad thing. It's just if the word sounds underdeveloped or is presented badly. LotR did this well, although the books read like a manual IMO. A Clockwork Orange presented words well, but some felt underdeveloped. Only some. I think Harry Potter did poorly in both cases. Of course, I only read the first book, and stopped there.