To be honest, the best thing about CPAN isn't any specific module, it's the sheer breadth of them - and the ability to install everything in a uniform way and have it usually work. Plus things like the cpantesters and cpandeps system that make it fairly trivial to tell if something -will- work on all the platforms you're targeting before you commit yourself to it.
Of course, if you describe yourself as "an old PERL programmer" you may have missed a lot of the recent cool stuff on CPAN - the binary is called 'perl', the language 'Perl', and the mistake of calling it 'PERL' kinda went out with the 2001-era CGI.pm crowd (this isn't meant as an ad hominem - I've simply found that anybody who says 'PERL' as anything except a joke is -hugely- likely not to have taken advantage of most of CPAN and have no way of telling if you're an exception to that :)
Of course, if you describe yourself as "an old PERL programmer" you may have missed a lot of the recent cool stuff on CPAN - the binary is called 'perl', the language 'Perl', and the mistake of calling it 'PERL' kinda went out with the 2001-era CGI.pm crowd (this isn't meant as an ad hominem - I've simply found that anybody who says 'PERL' as anything except a joke is -hugely- likely not to have taken advantage of most of CPAN and have no way of telling if you're an exception to that :)