Sometimes, it’s good to play to your players’ expectations. When you expect something about a game to turn out a certain way and it does, that can be quite enjoyable.
It’s like watching an action movie: stuff will blow up, the hero’s girl will be threatened, but he’ll win out in the end. In gaming terms, it’s fun when:
…orcs are always evil brutes.
…evil masterminds always employ elaborate deathtraps, rather than just killing you.
…the Big Bad is always in the last chamber of the dungeon.
…your NPC sidekicks never waver, happily marching into the jaws of death.
Those game elements are fun partly because they’re so familiar; there’s an element of nostalgia involved in encountering them, and seeing how your group tackles them keeps them different enough to be interesting.
Don’t shy away from incorporating the familiar into your campaign. Avoid using comfortable standbys as shortcuts, nail the details and your players are likely to greet them like old friends — which, of course, is exactly what they are.