"War never changes" is something like the eponymous video game tagline, a commentary on the stagnancy of human nature even in the face of cataclysm. Fallout takes place in a world built on pessimism and a game with an eye toward dark humor, and spawned a series of some of the best RPGs you can ever play (if I had finished Fallout 2 at the time of my making this list, it probably would have landed way up there).
The experience that made me realize I loved Fallout was during a quest that involved helping a sheriff bring in a small-town crime boss. When we made it clear that we would be taking him in, the crime boss and his enormous bruiser attacked. Just for humor's sake I shot the goon in the crotch - I blew away his manly bits and he promptly passed out from shock and blood loss. The crime boss critically fumbled when firing and ended up hurting himself very badly, after which the sheriff shot him in the face. Blood everywhere and a pat on the back for a job well done. Mundane, perhaps, but it showed the kind of black humor and absurd violence that was so passe in this insane universe.
And one of the Perks made it so that any enemy you killed, even if you used a dart gun or a pea shooter, exploded into a fountain of gore. What's not to love?