Have you played/enjoyed the following games?
River City Ransom
Streets of Rage
TMNT: Arcade Game or Turtles in Time
The Simpsons Arcade Game
X-men Arcade Game
If you have, then you'll know what you're getting from Scott Pilgrim vs. The World.
It plays just like those classics used too, they haven't changed much at all so don't expect revolutionary new gameplay. It's a simple brawler, with some light RPG elements, an excellent old school soundtrack and cool 16-bit type graphics. Most importantly the game is fun, especially if you can find a friend (or 3) to play it with you.
Also, if you're fan of the comics you'll probably get even more enjoyment out of it but it's not required.
Hope that helps.