There are infinitely many possibilities that could completely change the expected value of the wager. Here are a few examples:
Pascal's wager argues that you should believe in one of an infinite number of poential Gods, with no way of knowing which is true, and damnation if you guess wrong. There could exist a god that punishes only Christians and rewards everyone else.
There exists a god that punishes people who believe in him based on probabilities (such as Pascal's Wager). Lacking specific evidence about the nature of the true religious faith, there are an infinite number of possible requirements for going to heaven and avoiding hell.
There exists a god who punishes everyone who is not an atheist, and rewards atheists for not believing in him.
For Pascal's Wager to really hold up logically, one has to show that the Christian god is more likely than any of the infinite other possibilities. There is no a priori reason to expect that. The reason that Pascal's Wager sounds so convincing at first is that the Christian paradigm was common among Pascal's peers (and still is many places), hence the Christian god seemed plausible whereas other possibilities were not considered equally plausible.