The Power Level for the Game is the total number of Gate Cards in all player's used piles. If you see it on an Ability Card, it means that you can't play that card unless the Power Level of the game is equal to or greater than the Power Level listed on that card. This is only on Bakugan: Gundalian Invaders and Bakugan: Mechtanium Surge Bakugan cards. Some of the Battle Gear Reference Cards have Power Levels as well.
There are Advantages and Disadvantages with the Power Levels now. Because of the new Power Level Feature you can't play strong abilities that have power levels on the cards, but if you have cards like Dead Calm you can instantly stop your opponent from bringing Special Evolution Bakugan into the Game, for example, Quake Dragonoid needs a Power Level of 2 to activate his Reference Ability and if you use Dead Calm your opponent will need to wait a turn to bring his card into play, and when he does he needs to wait another turn to roll him. Also if your enemy gets a Gate Card called Poison Ground in there winnings you get an extra Power Level point.