It incorporated some sort of a voting system for users to vote on the flash material there, to decide whether the flash is considered good and should stay in the portal. The voting system is also linked to a user-ranking system, sort of like an RPG game with levels.
Although the voting process at Newgrounds is not 100% fair, it can successfully filter out the really bad flash submissions.
Newgrounds also spawned its own flash series by long-time dedicated authors. Overall, it is one of my favorite sites.