In film, genres say a lot about the content of the work. For example, watching a drama, a comedy, or a historical biopic are different experiences. These are classifications of content: Wikipedia classifies Django Unchained as an "action western drama" and Titanic as an "epic romantic disaster". Both of these works are films, but the content dictates the experience.
If we take a step back from these movie genres, there are the sub-categories of filmmaking, such as movies, television series, advertisements, documentaries, etc. These are categories that indicate the form: Django Unchained is an action western drama movie. Simply stating that Django is a movie doesn't give any information on the content of the movie itself.
Almost all current videogame genres indicate the form, or primary game mechanics, but say nothing of the content. These classifications aren't useless, but these purely formal categories are limiting the way videogames are compared and discussed.
Saying that BioShock is a first-person shooter doesn't give any information on its content. With current videogame classifications, BioShock is grouped with an enormous amount of modern videogames even though the experience they offer is radically different. Yes, it's an FPS, but it's the fictional setting, the philosophical questions, and the medium-transcending plot that differentiate the game. "First-person shooter" says nothing of these things. In fact, think of your favorite videogames. Does their "genre" effectively highlight why they're so great?
Videogames have evolved enormously in their relatively short history, but the way we classify them, oddly enough, has not. Example: the modern masterpiece BioShock still fall into the same genre as Duck Hunt. While it is true that they are both FPS games, no standardized genres exist to differentiate these radically different gaming experiences. Both games are FPSs, just like 1903's The Great Train Robbery and Titanic are both films; however, films are also classified into genres based on form, whereas no content-inspired genres yet exist for videogames (with a few exceptions, such as horror). It's high time videogames adopt a new genre system to accommodate the wealth of different experiences the medium can convey.