Decent game, but could be improved a bit.
The gameplay is what you'd expect from a Pokemon game: You talk to people, you buy items, you get challenged to a Pokemon battle and so on and so on. You play as a kid who goes on a quest to purify Shadow Pokemon, just like Pokemon Colosseum. And although the game starts out differently from PC, you go to places from the last GameCube Pokemon game. Even the game's battle system is the same. It's quite obvious.
The graphics, although they are quite nice, they are also recycled from the last GameCube game. Not bad, though. From the huge batttlefield (in the battle system) to the labs, there are pretty much no problems in the graphics.
The sound is also decent. There is new music, but there are no voice acting (why?) and recycled music from Colosseum. Otherwise, the sound is well done.
There can be some replay value for some gamers, but even more value for hardcore Pokemon fans. If you are a newcomer to the RPG world or the Pokemon series, you may or may not find enough replay value.
Final words: Pokemon XD is good in certain ways and is highly recommended to hardcore Pokemon fans. However, for gamers who played too much Pokemon and found it repetitive, the game comes in as been there, done that. Pokemon XD: Gale of Darkness is just another average outing to the Pokemon series.