When it comes to vectorization I usually use it for logos and lettering. Since to me that is the best way to use the program. However a good challange is always acepted and since this was also part of the Illustrator class so I really wanted to make the best of my currents abilities.
The task was to make a comic book caver, spine and back cover all in vectorization. This was the result:
What I can say of the illustration isn't as good as it would have been if i made it with photoshop or Sai were I could use the brush more freely. To me the cleaner and completed your original sketch the better the results because I really can see you taking too mane liberties while doing the vectorization.