Javascript has 3 serious, fundamental problems. The first is that it's a prototypal language that's been forced into looking like a class-based OO language. This leads people to confusion and frustration, much the same as if you were making a burrito and someone replaced your ingredients with pita bread and hummus. If you try to work against the grain by imagining that JS is just another class-based language you will end up thinking that it's some crazy mutant language that doesn't make sense. If you go into it understanding the paradigm and how to make the best use of it you'll get much better results.

The second major problem with Javascript is that it was prematurely standardized due to excessive pressure to ship during development, and thus has a lot of little mis-features and defects in the core language that haven't been fixed due to concerns about breaking backward compatibility. Luckily it's generally possible to avoid these areas of the language without having to compromise your code so it's just a matter of keeping to good practices and of knowing what to avoid.

The third problem is that Javascript is primarily a web technology where it is married to the DOM, and historically browser DOMs have been a mess: non-standardized, buggy, sometimes slow.

Overall the result is a language with a few landmines that need to be tiptoed around but that is still very solid in its fundamentals. Compare that with many other languages that are more polished and yet fundamentally limited in significant ways (such as Java's lack of closures, for example).

The wonderful thing about JS is that because of its expressiveness, power, and advanced featureset, using the language properly becomes a potent self-reinforcing feedback loop, jQuery is one of the better examples of this.