What does Google Closure Library offer over jQuery?

Edit: take a look at this youtube video it may answer some questions about Google Closure better.

Probably the best sources of information on google closure are project discussion group, wiki, doc pages, demos and a yet unfinished book by Michael Bolin that is now available from safari books site.

one thing I can tell right away - there is a steeper learning curve for closure vs jQuery but it may be well worth it due to the library's vastness, clear organization and the benefit of using it together with the compiler and the templating tool.

closure library in that respect is more like dojo than jQuery, and some concepts were borrowed from dojo, according to Michael Bolin.

google closure compiler uses JSDoc documentation system which simultaneously (if created by the programmer correctly) provides documentation and enables catching many errors at compile time.

while function names are more verbose than jQuery's, the compiler shrinks the code (using various optimization tactics) and the type checking will save a considerable time debugging the code, so time typing in the longer names is probably not an issue. At the same time longer names add readability.

library supports browsers running in the quirks mode so that scripts could be embedded by other sites using "quirky" html

library works with (but does not depend upon) a javascript templating system called soy that simplifies filling documents with content.

like jQuery google closure allows traversing dom structure with the string-based queries using a dedicated component of the library.

closure library relies on dot-delimited namespaces more like Java - a very strong organizational feature.

using such namespaces will incur overhead in uncompiled code, but in the compiled code those things are replace with short variable names.