It pays vastly more than Test and One Day cricket, has radically shifted the balance between batting attack and defence (including in the One Day Cricket played today) by making strike rates matter more than batting averages, has made superstars of players that would have previously been considered severely lacking in defensive technique, encouraged athletic fielding and made Indian franchises an attractive and lucrative destination for overseas players. And probably made generations of kids grow up not wanting to be bowlers! That's a pretty radical set of changes.
The reason Twenty20 was incremental was because it took an entrepreneur like Packer, with connections and money, to prove that cricket could even be changed in the first place.