It's a lot easier to write Mathematica than it is to read it. I've come up with some retrospectively-horrific functions that were intuitively easy to write - just keep piling on the functions, really. It's like the standard mistake when children learn maths of writing "If x=-1, then x^2+2x+1 = (x+1)^2 + 5 = 5" when they mean "x^2+2x+1 = (x+1)^2; then (x+1)^2 + 5 = 5": Mathematica makes it very easy to write in a completely unreadable stream of consciousness.
An ability to switch back and forth to a sort of "graph" view would be tremendously helpful, as most people tend to have a better ability to process visual information rather than a stream of text
> It's a lot easier to write Mathematica than it is to read it.
+1. And it gets even more easier to read (“read”? :-) when you can select pieces in FrontEnd, with multiple mouse clicks or a corresponding hotkey. I got so used to it that I actually developed phantom pains in my editing of Html or TeX (or whatever, for that matter).