Shock is nice because nothing is actually weak to shock. You get the benefit of stomping shields and the occasional DoT bonus without worrying about a baseline weakness, unlike fire or corrosive. It's a great element for your "default" weapon rather than filling a specialist role (though it is always nice to have at least one to put stalkers on notice).
Edit - As for slag, it's pretty amazing for bosses. The only element of grenades I generally use is slag. Using a slag weapon when solo to maximum benefit is hard though, just because the duration of the weakness is really short.
Edit - As for slag, it's pretty amazing for bosses. The only element of grenades I generally use is slag. Using a slag weapon when solo to maximum benefit is hard though, just because the duration of the weakness is really short.