I don't want to ask what is good about each language because everywhere you look each language is the best in some way. I want to know why each language is terrible and by Web Languages I mean those which are mature for Web Development, such as: PHP, Ruby, Python, Perl and any others you can think of.
Your question is ill-posed. None of these languages are inherently terrible. Terrible languages don't appear in lists like this.<p>If you have a very specific problem that you need to solve, it may be that one language or another is an especially bad choice. But in general all of them work. Indeed, the four which you cite are more similar than different.<p>Many people would agree that C++ is a relatively poor choice of language for most "web development" projects, and yet there are many fine web-based systems built in C++. The original Amazon.com was written in C++ and it didn't exactly fail:<p><a href="http://highscalability.com/amazon-architecture" rel="nofollow">http://highscalability.com/amazon-architecture</a>