Why do I dislike jQuery?
The initial design looked like a creative web programming experiment (and experimenting is a great way to learn, for sure).
But jQuery was touted as something of a general purpose solution to web scripting. Web authors having a very superficial and limited understanding of what they do, could now do things that they would have otherwise been incapable of. It was empowering to this class of developer.
However, for web developers who actually understand what they are doing, jQuery demoted our role from someone who employs a a broad spectrum of conceptual and problem-solving skills. With jQuery, knowledge of web standards, web browsers, OOD, and EcmaScript help as far as understanding what jQuery does. However, once that is understood well enough, it quickly becomes clear that jQuery isn't the best application of those technologies.
jQuery has many inextricable design problems. Fixing them will cause change propagation and upgrade problems. jQuery has had problems with recent IE browser releases, requiring users to upgrade and retest.
The overloading and typechecking adds needless internal complexity. The code is unreadable, hard to debug, and results in errors.
By confusing attributes and properties, jQuery has caused a lot of bugs.
About the author
jQuery was critically reviewed around 2007. The author (John Resig) participated in that thread, left the group, and kept his mistakes.