Certain games end up getting into a fantastic rhythm that entertain players for a long period of time. Other games get into a rhythm that gets so predicable that it kills the fun and flow of the game. These predicable rhythms can occur when a game has two drastically different mechanics and repeats them constantly with nothing new to separate them. The game soon feels like an A to B repeat and can fall flat fast.
In the first game of the Uncharted series there is a distinct flow of the game. Platform, shoot, platform, shoot. The game gets so predicable that once you reach the highest floor of a building you better reach for your gun because bullets are coming your way. This design forces the game to show how little mechanics it truly has and ultimately makes the game feel very boring and predictable.
Example: Assassin's Creed
Particularly in the first and second games in the Assassin's Creed franchise, this pattern of predictable pacing and repetitive missions/gameplay is evident. Half of the player's time seems to be taken up by either pushing through crowds or scaling structures; both of which only require one or two buttons to accomplish, and are mastered very early on in the game (and are hardly, if at all, iterated upon). This is punctuated by the occasional and seemingly interchangeable assassination or battle, brought on either by the player being spotted by a guard or from participating in a narrative-continuing mission. Consequently, these quests become mundane as one after the other of the same formulaic tasks are interjected by long, expository cut scenes reliably triggered every three assignments or so.
It's easy to get caught in the tide of these actions, but if one finds themselves disinterested by the theme it is all too easy to exhaust the fun and turn the game off.