String theory has proven quite useful for advancing the mathematics of theoretical physics and bridging it with mathematics in general. However, there are just too many variations of the theory with some people proposing as many as a googleplex of possibilities. Here are just a couple of the variations I've come across.
One is the idea the 3rd spatial dimension we observe is merely a holographic projection; thus explaining the nonlocal effects of quantum mechanics as an illusion of distance between particles. Then there's the "mirror world" variations where the properties of mass and energy are intimately connected to another universe. What appears to be the action-at-a-distance of electromagnetism in our universe is explained by something prosaic like size, shape, or momentum in the mirror world. Kind of like a puppet show where you just can't see the strings. And of course gravity can form the one bridge between the two universes through which it might be possible to communicate back and forth.
Anyway, you get the idea. The latest evidence for quantum mechanics doesn't help matters either suggesting a contextual view. For example even nonlocal effects have proven to be subject to Indeterminacy and one contextual theory proposes that whether the cat is perceived as dead, alive, or in superposition depends on the observer (ie-context). Some of these contextual theories don't even appear to have any metaphysical bias whatsoever making them useless for choosing among the more background dependent string theories. Between the added complexity of contextual theories and the number of possible string theories its frankly a mess.