I've written a few Text-Based RPGs, but they were in C...haven't tried such a thing in Perl yet, so take my advice with a grain of salt.

One thing you may want to look into is some OO stuff. It's really nice to take out the abstractions of rooms, players, and enemies...that kind of thing can help a lot.

You also may want to look into using something like the d20 Open Source game engine to base your combat on...this would obviously be way over the scope of this game, but maybe just take some elements from it to base things off of. One of the hardest things about making games is balance. Making sure it's not too hard or easy is difficult (how ironic!), and basing your work off of an established system may help.