Well, did the general audience thought like that when Bond's Quantum of Solace turned out to be an underwhelming movie ? No, the next Bond movie - Skyfall turned out to be the most successful movie ever.
Similarly, Iron Man 2 was not as well received as the first Iron Man movie, it did not get the same critical acclaim as the first one, but the next Iron Man movie, IM3 turned out to be the most successful IM movie.
Also, it's worth noting that despite the mixed and lukewarm reception of Superman Returns, Man Of Steel did well.
And lastly, Batman Begins was not exactly a huge block buster as it did not earn much still, we all know how much successful TDK was, so.