Okay, everyone, take a deep breath because this one's a doozy. Team Rocket's evil plans threatened first a major corporation and then an entire nation. Team Aqua and Team Magma's climate shenanigans threatened the whole world. When Game Freak went to make Diamond and Pearl, they looked at the villains they had written in the past... and apparently thought something along the lines of “now, how can we top that?” Answer: a villainous team whose evil schemes threaten - I kid you not - reality itself. And they plan it all whilst wearing the kind of bizarre silvery jumpsuits you expect of aliens in dated sci-fi movies and sporting ridiculous turquoise bowl-cuts.
So what are these sinister plans? There's a fairly nondescript sequence in Eterna City in which Team Galactic are stealing Pokemon for extremely vague reasons, leading to a battle with the second commander, an unambiguously female purple-haired twit named Jupiter. Although Team Galactic are making a nuisance of themselves in Eterna City by stealing Pokemon, you learn from Jupiter that this is not their real purpose there (which raises the question of why they would attract attention to themselves by doing it at all, to which the obvious answer is “because they're the villains, damnit”). They're actually in Eterna to research the town square's statue of a mythical dragon Pokemon, since their leader (like Maxie and Archie before him) is enamoured with the idea of using legendary Pokemon to gain power. You actually meet this leader, Cyrus, independently while traveling and don't immediately learn his affiliation. Upon your first meeting, Cyrus explains his belief that the universe was once perfect, when “only time flowed and space expanded” but has become imperfect because of the creation of living beings with emotions, and that this is the cause of all suffering in the universe. He later tells you that he wishes to create a new world, and that he believes the legendary Pokemon of Sinnoh can help him do that. Shortly afterwards, Team Galactic plots to capture three legendary Pokemon that live in three lakes around Sinnoh: Lake Valour, Lake Acuity, and Lake Verity. These are not the Pokemon Cyrus is interested in; they are in fact the personifications of the three aspects of spirit, the thing Cyrus most despises for being “incomplete”: Uxie, the embodiment of knowledge, Mesprit, the embodiment of emotion, and Azelf, the embodiment of will. Although you do get a chance to kick the snot out of the third commander, a pompous git named Saturn (whose hair is blue and forked, because the rules of Team Galactic absolutely forbid normal hair), you and your friends utterly fail to prevent the three diminutive Psychic Pokemon from being captured and hauled off to Team Galactic's office in Veilstone City. Being the glorious ten-year-old hero that you are, you bust in and release them, giving Cyrus himself a stern talking-to in the process, but for the umpteenth time you are too late to keep Team Galactic from doing what they set out to do – in this case, siphoning the powers of the lake spirits to create an artefact known as the Red Chain. With this chain in his possession and accompanied by Mars, Jupiter and a number of grunts, Cyrus sets off for Mount Coronet in the centre of Sinnoh.
So anyway, Team Galactic in a nutshell. They look absolutely ridiculous, but I think once you accept that, let's be fair here, this entire universe is pretty campy, I think they're alright villains. The premise is similar to that of Teams Aqua and Magma, with the charismatic leader whose promises of a grand new world convince many followers of various stripes to join him and commit terrible crimes in order to bring about the fulfillment of their vision, but I think Diamond, Pearl and Platinum do it much better. It's easier to believe that people could be taken in by Cyrus's rhetoric than by Maxie's or Archie's - because his dialogue is just better-written. The issue with this plot is one that's been gradually creeping up on Pokemon since the beginning: scale. Mewtwo had phenomenal psychic power and could shred most other Pokemon in battle with ease. Lugia could cause hurricanes with a single flap of its wings and Ho-Oh could raise the dead. Kyogre and Groudon could alter the very structure of the earth's surface and Rayquaza was more powerful still. Dialga and Palkia take the cake, though, with the power to unmake the universe by dissolving space and time themselves. You fight these Pokemon and win. Then you stuff them into tiny little balls and make them do your bidding. I love Pokemon, but... this is getting ridiculous. That's not entirely Team Galactic's fault, though; as I said, I think they're better-done than their immediate predecessors and pretty good as Pokemon villains go. As for the new content in Platinum... throw out the whole Charon subplot because it's stupid and spend the time and money making the Distortion World a bigger part of the game. That is all.
I'm on the home stretch now... only one villainous team to go; the new kids on the block, so to speak: Black and White's Team Plasma.