It's a decent shooter that got not-so-decent reviews (as most shooters do by mainstream reviewers). It's lacking in several departments though, such as being able to change your weapon without having to tap the screen and somewhat bland gameplay (uninspired enemies, few obstacles, no power-ups). It's also a fairly short game that's quite low on the difficulty scale.
If anything, it's a great example of how nice games can look on the DS (slightly better than PS1). Too bad the R-Type series is dead and Konami seems more interested in porting Gradius over to the PSP rather than the DS. Darius has been MIA for a while now and I'm not a big fan of Treasure games. Vertical shooters are also an era of the past, though I wouldn't mind if ZUN ported one of the Shrine Maiden games to the DS (if that ever happens though, my DS will be permanently fused to my fingers).