I will admit that, as a film genre, I am not the biggest fan of musicals. I found the yearly-ish Disney animations of my youth frustrating. How did all the animals happen to know the lyrics and dance moves of a seemingly spontaneous performance? In live-action musicals like The Sound of Music, why didn't anyone else find it odd when people broke out in song? Because I failed to understand that the rules and conventions of the musical genre as being more important than a coherent fiction for these films, I could not enjoy them.
Reflecting, the frustration my parents expressed the few times they tried to play videogames with me through my childhood are quite similar to those I felt towards musicals: "Why did that item disappear?", "I shot him! Why is he still alive?", "How am I carrying so many weapons?", "Why can't I just use the blue key that I picked up on the last level?", etc. Just as I failed to accept understand the rules and conventions that lie at the heart of the musical film genre, inexperienced gamers will feel frustrated when a game's fiction inevitably breaks coherency and falls back to rules and conventions.
Both musical films and adventure games (by which I broadly mean character-driven games centred around the eventual resolution of an arbitrary plot) present, exploit, and abandon narrative elements in similar and parallel ways. While a musical film consists of song and dance performances generally separated by non-musical scenes, an adventure game consists of playable segments generally separated by non-playable cutscenes.
The performance in a musical film acts in the same fashion as the playable segment of an adventure game. Neither is required to move the narrative towards its conclusion, but that does not meant that it can't. Performances in musical films are split broadly between 'integrated' and 'non-integrated' performances. An integrated piece does move the narrative forward, but a non-integrated performance simply adds to the style and tone of the film without necessarily moving the narrative towards its conclusion. Non-integrated performances are still entirely justified as musicals are primarily about music, not storytelling. The playable segments of the adventure game can also be defined by this binary. An integrated segment will push the narrative forward, while a non-integrated segment could be just another platform level. Non-integrated playable segments are still entirely justified because games are primarily about playing, not storytelling. However, while storytelling is not the primary concern of either musical films or adventure games, both still indeed use stories and narrative in very similar ways.
(It is worth noting that 'integrated' and 'non-integrated' are merely the two extremes, and most playable segments and musical performances will indeed fall somewhere between the two.)
Similarly, the non-musical scenes that separate performances in a musical film act like a game's cutscenes. Non-musical scenes rely on fictional coherency (that is, the social and physical rules of the presented world are consistent) to push the narrative forward at least enough to instigate and justify the next musical performance. In the same way, an adventure game's cutscenes abide by a fictional coherency often ignored during the playable segments to push forward the narrative enough to instigate and justify the next playable segment.
Both musical films and adventure games use rules and conventions to justify breaks in fictional coherency. While the non-musical scene of a musical will be coherent in its application of normality, the moment the characters begin singing and dancing, this coherency is abandoned, justified instead by the convention of the genre that people must sing and dance in choreographed performances. Games, too, fall back on rules and convention to justify a lapse in fictional coherency during playable segments. To a gamer unfamiliar with the conventions of third-person platformers and action games, watching one bullet cripple Nathan Drake in one of Uncharted 2's cutscenes after the last two hundred bullets seemingly had no effect could be very frustrating. While the cutscene relies on the fictional coherency of the presented world that bullets hurt, the playable segments rely on the game's rule that health will recharge over time if the player is not shot again straightaway.
These parallels that adventure games (still a relatively young form of presenting stories) share with musicals (an older, perhaps more confident genre) are worth acknowledging for a variety of reasons. Just as all musical films use a blend of integrated and non-integrated performances, we can learn how games could better integrate some playable segments while also justifying the inclusion of non-integrated segments within the same game. In other words, the story can be progressed during gameplay, but gameplay that doesn't progress the story is no less valid.
For me, playable segments sitting at the non-integrated end of the spectrum would be the long grinds in an RPG like Final Fantasy VII, the repeated corridors of levels like Halo's Library, the jungle-gym climbing sections of Uncharted 2, wandering Fallout 3's wasteland between quests. All of these sections are fun (though, some will disagree with my Halo example), yet none, in my opinion, explicitly move the plot towards completion. More integrated segments would be fighting Sephiroth, blowing up the Pillar of Autumn to destroy the Halo Ring, sneaking into the Turkish Museum, leaving Vault 101 for the first time. These segments are playable and progress the story. These examples are, of course, subjective and open to much debate. It could be argued that every step taken in every game progresses the plot and is an important action to the overall experience, but that does not invalidate the theory--it could also be argued that every song of a musical brings us closer to the end of the film.
I still do not watch musicals often. However, as I am now more appreciative of the genre's rules and conventions as fundamentally more important than fictional coherency, I am able to appreciate the genre. Musicals such as The Sound of Music and Sweeney Todd show that a musical can be constructed on any ration of integrated and non-integrated performances to present a vast variety of themes. Games too, just like musicals in their own youth, are capable of expanding to present a far a broader variety of themes than they currently do. Certainly, many early musicals conformed to the 'backstage musical' structure of characters putting on a show merely to give an excuse to perform lots of songs and dances, but are the blank-slate space marines of adventure games today any better?
Perhaps by looking at how musicals take advantage of narrative when it is needed but ignore it when it is not needed, games may learn to exploit narrative in a similar fashion to craft more creative integrated playable segments, but also to grow more self-confident to accept non-integrated playable segments that don't forward the plot, but don't have to either. Ultimately, analysing the punctuated story progression of musical films would be more useful for understanding how game stories progress than looking at more traditionally linear genres.