Metroid prime had a great story, or at least a workable one. Some space pirates were performing nefarious acts and you must stop them while taking on some sort of evil presence on a planet. Having the space pirates as a focal point, then realizing that they were only a part of a larger scheme was great. Not so in mp2.
You resume your role as samus aran, a bounty hunter (and apparantly universal do-gooder) who recieves a distress signal and goes to investigate. When you land on a planet, your ship is damaged and slowly repairs itself while you go about your business on the surface. The planet has actually been at war for some time now. It began when a meteorite crashed into the surface and split the planet between two different planes of existence, light and dark. Since then, little wormholes allowed evil beings called the ing to cross over, possess creatures, and generally cause problems. The original inhabitants were perturbed, and sent their own armies through to the other side. They were essentially pulverized and found another way of defeating them. They created a device which allows you to steal energy from the other side and bring it back. This energy apparantly stabalized the world, and if one side had all of it, the other would be destroyed.
And guess who gets to go get if for them!
The space pirates are also here, but they're resigned to being shot at, possessed, and destroyed by the ing. They're the whipping boys for every little creature on the planet. There is also a dark samus wandering around, who likes to steal phazon from the pirates, which they use for power and she uses for god only knows what. And if you're wondering about that distress signal, that's the marines from...some government or other...
Enough with the plotline. The game plays just like the last one, but you'll notice some differences immediately. For one, the controls are tighter. Free look is easier to use and samus maneuvers in a crisp, easy fashion. Scanning is also better, as instead of just having an icon which changed depending on whether or not an object was already scanned, the entire object changes color. Green for already scanned, orange for scannable, red for logbook stuff, and blue for stuff that moves. Switching to the scan visor, you can look around the room and instantly see what you've scanned. It's very nice.
Speaking of which, again there is alot of stuff to scan, though not quite as much as the last game. Previously, practically every microbe you see is scannable. In this iteration, sometimes little birds or crabs will go by, and you will be confused by their inability to be scanned, while a piece of grass sticking out of a hillside that doesn't actually do anything has its own entry. Wierd. Although the space pirate entries have become alot more fun to read. (Metroids are NOT pets)
As you probably have guessed, at some point you start going through the portals to the dark side. It's a bleak world over there. The entire planet is a poisonous mess and simply touching the air causes damage. Fortunately, there are bubbles of protective light which also recharge your health bar. So if you ever get too much damage, you can find a quiet bubble, go get something to eat, and come back ten minutes later with full health. Alot of puzzles also involve going between sides. Sometimes you simply need to activate something on one side, sometimes it requires multiple trips. But anytime you have to do that, it's usually worth the goody you get at the end.
Your weapons have also changed. No longer do you have the ice, wave, and plasma beams. Now you have the light and dark beams along with another that uses both energies. Also, you have ammunition now. It seems like a hassle at first, because shooting something with the light beam gives you dark energy and likewise with the other, but it's actually a good idea to use as much ammunition as possible because using ammunition almost always gives you more ammunition than you used, in addition to more health and missile poweups. It makes the game more interesting.
The light beam is great against dark enemies, simply plowing through them with ease, but the dark beam is so-so against light enemies. Quite frankly, there's not really anything light that's bad enough to be too much of a problem for you. Even so, there are one or two enemies I like to use the dark beam on if only to get light ammo.
Also, the superweapons are useless. When I say useless, I mean you waste 30 beam ammo and 10 missile ammo, and might get one or two enemies if you're lucky. Both light and dark superweapons fire a slow-moving projectile that does cause alot of damage, but due to enemies becoming temporarily invulnerable almost all the time, you just can't cause all that much damage. It's terrible. However, the third superweapon is real nice...
Speaking of enemies, alot of them make a return. You'll see those suicide bats, exploding wall crawlers, and yes the space pirates. They all get worse when taken over by the ing, so it's usually a good idea to take them out as quickly as possible even if they don't seem so bad now. Too many of these guys, especially the bosses, become temporarily invulnverable far too often. You might damage a boss enough so he cries out in agony, but while he's roaring his head off you can't damage him even if you fire a supermissile right into whatever weak spot you had. You have to learn exactly which animations allow you to damage enemies, which is intensely annoying and takes you out of the game.
The graphics in this game are beautiful. Where the last game had stunning landscapes, this one has stunning landscapes with more detail. Slowdowns are few and far between, so the cube handles this one quite well. Compared to the last incarnation, everything is more solid looking and a tad more serious.
The much vaunted multiplayer in this game is a big letdown. You go around, lock on to each other, and dodge shots. Getting away as a morph ball is great fun, but even with that there's just not really much here. One level even includes a massive turret which might as well be invulnerable, with all the damage it causes. It's really too bad.
MP2 is a game which improves upon its predecessor in some ways but loses quality in others. The light and dark story, while not exactly original, does make for some interesting puzzles and a world which is twice as large. All in all, you'll enjoy this game if you buy it, but even with multiplayer the replay is not great.