There is considerable variation across different beers, and this means that differences between beers are an important component of the characteristics of those beers. The taste of beer is highly subjective and people will interpret the taste of a different beer differently depending on their own personal perspectives.
While individuals might differ in the way that they view a given beer or what tastes they consider to be more desirable than others, there are some key flavors to look out for that should not be in beer and are an indication that there is a problem in the beer.