Great addition to the Metroid Prime history and more action than the first!
The game plays exactly the same, but the visual are somehow improved and some enviroments are more detailed, also, you can travel forth and back in most places and see how they look in the light or dark world. The game menus are totally redesigned and, although may seem a little more complicated to handle, the information contained is also better organized.
The first MP required an enourmos amount of things to be scanned and, sometimes, it was easy to lose some of them. Now there is a easier to track list and easier to check when you're missing something.
About the history, you'll find pirates and metroids, even a new dark mutation, but the real bad guys this time are called the Ings, which are trying to take over the planet and have almost vanished the light race, called the Luminoths.
This time there are more cinematics to help you understand what happened, and some Federation troopers take part on them -later you'll find only their bodies but hey, this make wonder why we don't have a shooter with those characters!
The problems grows when you encounter for the first time Dark Samus (Hunter), which appears to have a deep relationship with the phazon lying in the dark part of the planet. Be prepared to fight and be, somehow, hunted by this enemy.
MP2:E, is such a great game as the first one, and it even adds a Multiplayer which can be, actually, pretty fast and fun, but nothing special. In any case don't lose the opportunity to meet both MP titles before playing the upcoming Wii sequel.