Look at [link|http://www.rubycentral.com/book/builtins.html|http://www.rubycentr...ook/builtins.html] closely. This is Ruby's libraries, which seem to do a very good job of abstracting a lot of what is good about a scripting language into a fairly cleanly designed library. Essentially, "Perl as a class library." You might get some useful ideas from browing that.
The most major thing that I think is wrong in the class structure is that it would have been nice if it was designed with something like [link|http://artengine.ca/matju/MetaRuby/|http://artengine.ca/matju/MetaRuby/] in mind from the start. What that is is a series of mixins whose purpose is to make it easy to implement a new data type which happens to resemble one of the basic built-in ones. (Think Perl's tie - only it falls out of the design of the language...)
Cheers,
Ben