At a crucial moment in the middle of an tense, violent battle, a major character in Snowpiercer slips on a dead fish like a banana peel. During a violent chase sequence, another character frantically steals piles of addictive drugs (and a bottle of wine) from random passersby. Compare these bursts of manic silliness with the fight sequences in, say, the Dark Knight trilogy: Unless the Joker is involved, they are a flurry of faceless stunt doubles (or grimly determined actors) throwing punches over stiff shoulders.
Snowpiercer owes its sense of humor in part to being so influenced by the wild sci-fi of Terry Gilliam, but it also proves a rule that many modern sci-fi or fantasy movies forget: Just because your setting is grim doesn’t mean you shouldn’t crack a joke once in a while, or be playful with action and scene.
For a study in good versus bad approaches, compare the first two Terminator films to the fourth, Terminator: Salvation. The first movie is a brutally efficient thriller that still has time for a couple great, twisted laughs (“Your clothes. Give them to me.” and the endlessly famous “I’ll be back”); the second movie has a much lighter tone with the playful interaction between John Connor and the Terminator. Salvation, by contrast, is so interminably grayed-out (in aesthetic, dialogue, and pacing) that it is impossible to care about what’s going on, or why.
Note the other main difference between these two pairs: You care what happens to the main players in the first two movies. Humor is humanity; we laugh to grapple with great despair all the time. Failing to consider the two in equal balance leads to something leaden and stiff. Many modern blockbusters seem to be inspired by noir (by way of Batman, no doubt), but forget that pulpy fiction is pulp because it’s fun, not because it’s dark and edgy, but because it can be demented and playful (and, therefore, funny) in a way that more wholesome entertainment can’t quite match.
The average modern Marvel superhero movie, incidentally, runs circles around its DC Comics counterpart primarily because levity and color are important parts of the formula. For my money, honestly, 2004’s Spider-Man 2 is still the pinnacle of the pulpy superhero genre; thanks to particularly inspired direction from Sam Raimi, the film asks the audience to laugh about as often as it gasps or cries.