Well I think the biggest thing to consider with Gruber is that he never really made a mistake. That's one of several things that made him really special. He wasn't done in by doing something contrived, stupid, or inconsistent with his character. He had a perfect plan, could not have predicted a loose cannon like John McClane being a part of it, and successfully improvised against everything John did right up to the end. There's no way Hans could have anticipated the duct tape gun, and even after that, *still* almost blew away either John or Holly before they got her bracelet off.
He oozed charisma and class and by his own shockingly consistent competence made McClane one of the great action heroes of cinema.
I strongly recommend that you give Die Hard, and Gruber, another chance.