[Diplomatic Hat On] I would personally stick with a Scheme or with one of the better CLs (SBCL, etc.) over newLISP.

NewLISP is interesting for the space it occupies and it can be fun, but it also has some really wonky ideas that I think are mistakes and that will make it more difficult for you to grok other Lisps in the future. It is not a horrible language, but I think a person's time would be much better spent learning another Lisp. I would suggest that you Google comp.lang.lisp for newLISP. That should provide you with plenty of 'criticism' to digest. Several other people have asked the exact same question before on comp.lang.lisp.

Then, go to: http://gigamonkeys.com/lispbox/ once you've moved on ;-)