Used to play it with my brother and, as soon as we finish, we started playing again :D
It is highly addictive, even thou you fight against just the same enemies, but with different collors! It's hard to explain, you just start amashing the buttons and keeping the high scores to get more lives.
There are also some hidden itens that give you extra lives or replenish (some) of your health.
The music is also great. They really push you to keep playing and pumping the buttons of your controller.
The synthetized voices and sound effects are also cool, and fit for the characters and enemies (despite the enemy women screeming like a whistle :P).