(Saw a lot of topics on Digimon games, so I figured I start this one.)
Needless to say, Digimon Dusk/Dawn is a lot like the Pokemon games. Dusk/Dawn, Blue/Red?
Each game follows the same story but from a different perspective. Certain Digimon are unique to each game, too; including the Digimon you start with.
I only own Dusk but it's really an enjoyable game, and since it's on the DS it's also portable. Most people who played it will probably say that it pales in comparison to the Pokemon franchise, and maybe they're right, but for any fan of the series this is a real gem.
The only complaint I have is the random battles. Once you're inside a dungeon there are no safe zones, and you enter a battle every three steps. It can become frustrating.
My favorite feature on the other hand has to be the evolution. Each Digimon has more than one evolution path, each path branching off into more as you go along. And you can always de-evolve if you wish to try something different, gaining a stat bonus when you do.
The story is predictable and a little lame, the quests are redundant, but raising your Digimon is fun and addictive.