Digimon Story/Digimon World DS, among Digimon fans, has been called one of the greatest games in the series (not saying much, however). I haven't played it, however, I have been tracking it since release in Japan. It plays like Final Fantasy, and is very similar to Digimon World 3/2003 (it has been called the best in the series, again, not saying much).
It features over 300 Digimon, including Lalamon, Gaomon, and other Digimon Savers Digimon. While it has Wi-fi connection, it sucks. There are no trading or battling online, simply matching Digimon. However if you know someone else with the game, I believe you can battle and trade.
There are some very strange Digimon lines (i.e. Rapidmon -> SaberLeomon, Antylamon -> ChaosGallantmon).
Sprites are similar to Digimon World 3/2003, but cleaned up.
It really depends on if you're a die-hard Digimon fan or not. If you are, you might want to give it a shot. If not, stay away from the game.
It's promoting Digimon Savers, which (hopefully) will be dubbed some time in 2007
But as BattleFranky~40 said, there will plenty of better games out.