They're about the only thing that's stayed the same. At the center of each maze, four ghosts begin to chase Pac-Man as he attempts to raise his score. Eat a power pellet and you can chow down on said ghosts, earning more and more points while you do. The new bit here is that you can actually string power pellets for multiple point bonuses on each ghost.
Pac-Man Championship Edition is awesome, but just doesn't feel like a full game. It feels like a bonus mode to a more full-featured title. Had Namco even, perhaps, included the option to play the classic Pac-Man upon downloading C.E., things might be different.