I felt the need to rant, so why not? :)

Nest types suck

In perl you can't do anything obvious like create a hash of a list of strings trivially, you have to spend your entire time worrying about references. Why? I don't know.

A Gazillion obscure operators and magic variables

In perl you're never sure the operator this person is using is. Perl has operators and variables names after almost every punctuation key on the keyboard. (Pop quiz: Which punctuation keys on a standard qwerty keyboard, aren't valid perl variable names?)

Simple things are hard

Someone once said that the definition of a low level language is one that requires you to spend your time worrying about the irrelevant. Perl must indeed be a low level language. Trying to figure out how to pass a list to a function, create a local variable in a function, nest types are all things that are difficult to get "right". You have to know a magical encantation to do them. Why don't they do the right thing?

Theres More Than One Way To Do It

Perl people say this is a good thing, but the problem with theres more than one way to do it, is that noone ever does it the same way twice. To properly read a program you have to understand the 'idioms' that that program is written around. In Perl it's difficult to realise that "ah, thats a switch statement, I can see what that's going to do" because in perl there is no switch statement, you can roll your own (a nice idea), but, you can get half way through and discover someone's modified their idea of a switch statement slightly and now it has a side effect you didn't realise until you read the code very very carefully. In most languages you can learn a couple of constructs (for, while, do..until, if...then...else, functions) and you've learnt a good chunk of the language and can read most of it. (Even C++ which has a huge number of things (virtual private classes? who on earth would use such a thing?) you learn about the various flow control structures, and how to define/call functions/methods, and you can follow a good chunk of C++), however in perl, since theres so many ways of doing anything you have to learn all the idioms before you can read a sizable chunk of perl code since they are all used, randomly.

Cause doesn't always preceed effect.

Perls operators like "unless" mean you can spend a long time reading a block of code before realising that the entire block doesn't get called because there is an "unless" at the end of it. Cause should preceed effect, not come half a program later.

Perl implicitly does things behind your back.

Perl's $_ operator saves a lot of typing, but makes your program have a large hidden dependancy. Like the "more magic" switch of lore, changing something unrelated that does absolutely nothing obvious can cause your program to crash. Is it safe to insert some code in the middle of this block? Who knows! It could disrupt the fabric of space time that this perl program exists in.