The object declaration is painful, it has variable hoisting and doesn't have proper block scope leading to all sorts of weird bugs, it doesn't have simple namespacing, it didn't have a foreach, it didn't have get/setters until recently and even now the syntax is bad because they wanted to maintain backward compatibility.
Oh and everything's a bloody function. A function is a function. A class is a function. An anonymous method is a function. It can get really hard to read and pick out what a bit of code is actually doing on first pass.
And that's just the big, really simple but important, every day stuff that a normal coder needs to do their job in even the slightest complexity scenario.
I sometimes wonder if the 'other' language that netscape was going to use was really as frustrating as javascript is when you start working on more complex code.
What it did have which most languages didn't have is treating functions as first-class objects and closures. They're brilliant.
Unfortunately almost all other modern languages now have these and javascript still doesn't have all the other goodies so that's one of the many reasons it gets so much hate.
So now compared to any other language it looks so dated and archaic.
I really enjoy writing javascript at times, but as the code gets complex I despise it. And I hate coming back to my old javascript code.