Pokémon XD: Gale of Darkness is the successor to Pokémon Colosseum and is another third-generation spin-off from the main Pokémon series. It was developed by Genius Sonority and published by The Pokémon Company exclusively for the Nintendo GameCube in 2005.
Pokémon Colosseum was developed by Genius Sonority and published by The Pokémon Company in 2003 in Japan and 2004 everywhere else. It is not considered part of the main Pokémon series, but is a third-generation spin-off made exclusively for the Nintendo GameCube.
While I wouldn’t call myself a Pokémon fanatic, I do really enjoy the games because they are so well made, and because I love level-grinders. Pokémon Pearl (and its companion, Diamond) is considered by many as one of the best games in the series, and people still love to play it now.
Compared to previous generations, Pokémon Pearl has lots of new features, and compared to later generations: the series hasn’t yet started to collapse under its own weight.