You would think that it would be hard for the Dreamcast to follow in the 2D footsteps of its sibling, the Sega Saturn and its massive collection of 2D shoot-em-ups. However, the Dreamcast is the perfect complement to the Saturn and is a essentially a requirement in and shmup fanatic's collection.
While it only started out with a few shooters from Psikyo and Capcom (most of which looked like nice 2D Saturn games), it gathered quite a library by the end of its life. In fact, MOST of the 2D shooters for the console were released well after the Dreamcast was "dead" in the United States.
So yes, if you wish to play most of these, you will need to learn how to play Dreamcast imports. But if you are a shooter fan, you will not regret investing in some of these Dreamcast gems.