You're right. It is a little unfair as there is a degree of type casting for which Willis cannot be blamed. He plays to his strengths maybe. As you say, he was as good as he gets in Twelve Monkeys and, to a lesser extent, Pulp Fiction. Trouble is, for me anyway, whatever character he plays I always see Willis. That distinctive smirk he has just reminds you. Not his fault, and arguably harsh of me, but nonetheless. Makes me feel he just plays variations of himself. But, as you rightly point out, there are no shortage of actors that do that!