The move busting Bust-A-Move '99 was the first 4 player Bust-A-Move game in the series. For the N64, at least. The core gameplay has basically remained unchanged. You know there's not much new when one of the special features is "New backgrounds".
Your team of too-cute dinosaurs maneuvers an arrow that points at multicolored bubbles at the top. Wherever the arrow points is where it will shoot a new bubble when you press A. Three bubbles touching each other will make them all fall down, gaining you points, and raining pollution on the enemy. The bubbles are actually enemies from Bubble Bobble trappedin the bubbles that the dinosaurs threw them in. So that's how they dispose of opponents.
Down the road new colors will be added into the mix to make matching them up even harder. There are those damning gimmick bubbles too. Some are unbreakable, meaning you'll have to cut out the bubbles around it to make it drop. Some help get bubbles down faster.
All the while, the bubble wall at the top keeps getting bigger and moving downwards, towards our dinosaur friends. If they reach the bottom, it's game over.