Since we're talking about ads...
I miss video game commercials from the 90s and early 2000s, where a smoker-voiced narrator would actually give you a brief description of the gameplay and there would be some ridiculous skit bookending it.
Here's my shot at a corny but informative 90s-styled ad for SSB4:
[COLLAPSE='Go ahead and laugh!']
Kid 1: Whatcha playing?
Kid 2: Super Smash Bros!
[Gameplay footage of Mario appearing on-screen.]
Kid 1: Cool, it's Mario!
Kid 2: Yep, and Sonic's here too!
[Gameplay of Mario vs. Sonic, then a montage of other characters.]
Kid 1: Wow! And Pac-Man, Donkey Kong, Pikachu and Zelda!
[Kid 2's mother and father show up, each holding a different kind of controller.]
Kid 2's Mother: Boys! How about a two-versus-two!?
[Skit takes a break. Pure gameplay montage set to the game's main music theme.]
Gravelly-Voiced Narrator: It's Super Smash Bros! Up to four players can duke it out using Nintendo's finest fighters. Build up your opponents' damage and send them flying with a devastating Smash attack! Super Smash Bros. for Nintendo 3DS now available. Super Smash Bros. for Wii U launching this holiday. Online interactions not rated by the ESRB.
[Gameplay concludes with Mario launching a MARIO FINALE!]
[Back to the four players on the couch, their hair blown back and everything around them scorched.]
Kid 2's Father: ...Best two out of three?
Gravelly-Voiced Narrator: It's a Smaaaash!
[/COLLAPSE]
And yeah, for that route I'd have the main theme play in the ad during the gameplay.