Like many sequels, Prime 2 does not best the original, but it still is an impressive addition to the series.
Story
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Metroid Prime 2: Echoes's story is more or less interesting. It is somewhere between deep for a Metroid title and just as shallow as a Metroid title's story should be. This time around, Samus crashlands on a mysterious planet called Aether, leaving a decent explanation for why Samus can't simply leave because she wants to. As for the whole connection to the entire Metroid series's storyline, there is barely any besides to introduce the entity that is Dark Samus and to further prove the dangers of the deadly toxin introduced in the original Prime game as Phazon. Echoes's story revolves around a philosophical race known as the Luminoth. These peaceful creatures recently endured a war and seemingly lost to their enemies, known as the Ing, until the sole survivor, U-Mos, appoints Samus to finish the Ing off for good and bring peace back to Light Aether. See, a meteor, later proven to be a Leviathan Seed, awkwardly crashes into Aether, splitting it into two separate dimensions, respectively called Light Aether and Dark Aether. It doesn't take Samus long to realize that if she does not fulfill U-Mos's request, Light Aether will be destroyed, and then the Ing will terrorize other planets, including those such as Daiban. Light Aether is as normal as any Metroid environment, but Dark Aether can prove to be hell, as the atmosphere literally corrodes your armor---at first. Story: 8.5/10
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Graphics
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Okay, these graphics are abso-freaking-lutely AMAZING for a GameCube game. They are almost beyond Xbox-level in terms of shininess and what not---they definitely surpass games like Halo: Combat Evolved in terms of graphics. They certainly kick the crap out of the original Prime game's graphics. The animations are, as expected, wonderful. The only issue many people including myself have with the graphics is the assortment of colors. There isn't much variety at all in either world, but especially in Dark Aether. But graphics are most definitely not all that matter in a game, are they? Graphics: 10/10, for its time.
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Gameplay
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This game is, by all means, NOT for the casual gamer. Why? Well, first off, it's hard as hell. Boss after boss sans a few are ridiculous in difficulty or time wasted trying to beat them, or both. For example, the Boost Guardian. One of the three most annoying bosses in the whole game. You fight it in Dark Aether with NO safe zones, so your health is slowly corroding away every second of the battle. Albeit, unless you sequence broke the game, you should have the Dark Suit by then which makes the corrosion rate significantly lower than before, but this fight is still hell. I won't go into details, as this isn't a boss guide. But I will tell you this: the game is satisfyingly difficult for the most part, with some ridiculously tough areas to trudge through.
As for bosses, as said, most are difficult, some take too long, some are pushovers, and some are pretty damn epic. I'm eyeing Quadraxis with that remark; Quaddy is quite simply the best Metroid boss in any Metroid game if not among the best bosses in video gaming history.
The game plays pretty much the same as the original Prime, with a satisfying number of new upgrades including beams, visors, suits, etc. Gravity Boost, for example, is the equivalent of the original Prime's Gravity Suit, however, it also allows Samus to jump three times underwater with the third time open for being a very long thrust upward. This upgrade is practically useless anywhere else besides the hydro-station section of Torvus Bog, but it is still very fun to use. An upgrade that was not used in the original Prime but was often obtained late in all 2D Metroid games is the---drum roll please---Screw Attack! Yep, that's right. Retro brought the Screw Attack and very nicely transferred it from a 2D item into a 3D upgrade; something thought to be impossible by many with an item such as it. Gameplay: 9.5/10
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Sound
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While much more dull when compared to the original Prime's phenominal musical score, Echoes's is still great in almost every way, particularly in areas such as some boss fights, Torvus Bog, and Sanctuary Fortress. Quadraxis's theme is the meaning of epic, and the Emperor Ing's themes are very fit for the mood that is attempted to be set by Retro. The sound effects are everything you'd expect for a 3D game. Sound: 9/10
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Length/Replay Value
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This game is considered to be very long--perhaps too long--for a GameCube game. It will take about two days to beat it if you play it very religiously. As for replay value, there isn't much. You aren't too likely to start a new file just because--mainly due to the fact that the game is very long and tiring at parts. Length/Replay Value: 8.5/10
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Fun Factor
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Don't get me wrong---Echoes is by all means fun. At least, the story mode is. It has a half-baked multiplayer which is no fun. For one thing, it gives too many cheap advantages and few weapons to fend enemies with. If you're good at Unreal Tournament or Halo, that doesn't mean you'll kick ass at this multiplayer. There are few maps to play on. Ultimately, don't get Fun Factor just for the multiplayer, because you will get heavily disappointed by it. Get it for the awesome single player mode. Fun Factor: 9/10
Overall: 9/10, superb. It doesn't beat Metroid Prime by any means, but this game is most definitely worth your money if you are interested in the genre.