I honestly didn't do much with imports on the Dreamcast. I imported...some Giant Gram game for the DC but honestly I didn't get into it and sold it later. It didn't grab me like the AKI games did. However, I did also get the Dreamcast Fire Pro game. Still, the Saturn had Six Men Scramble, my first Fire Pro ever, so it's a bit of a sentimental favorite.
Beyond that, there wasn't much. There was Puyo Puyo 4 and Ikaruga/Border Down which I ended up getting a bootleg of after the DC had been discontinued, and that's it, I believe.
Granted, I wasn't as driven to import with the Dreamcast since I found the domestic library much more satisfying. What other DC import titles are great (and hold up)?
EDIT: oh, come to think of it, I imported a PAL Shenmue 2...which failed to capture my interest, just like the first had. Ultimately I sold it.
Your mileage may vary.
It's too bad Sega apparently dropped the ball with Fighting Vipers 2 (it sucked, apparently, and it was kept from the U.S.). They did have Virtual On: Oratorio Tengram on DC as well, although it was of course a highly compromised port, control-wise. However, provided you're using a custom controller/stick/a non-crap controller, the DC had one of the best fighting game lineups for any system:
Soul Calibur
Power Stone 1 and 2
MvC2
Capcom vs. SNK 2
Darkstalkers Chronicle (import)
Last Blade 2
Garou: Mark of the Wolves
Project Justice
DoA2
Street Fighter 3 Third Strike (+ Double Impact)
Street Fighter Alpha 3 (okay, kind of a crap port, but still playable)
Virtual On: OT
Guilty Gear X (import only, I think)
King of Fighters 98
King of Fighters 99
King of Fighters 2002 (import)
Tech Romancer
Virtua Fighter 3
Super Street Fighter X For Matching Service (import)
The only thing that comes close is current gen systems that have compilations, download versions of the games, and sequels available. Granted, not all of the above are exactly tournament material, but still were strong/fun titles in their own right.
Something I can't quite wrap my head around with the Dreamcast, though, especially with all of the progressive moves Sega made with it, was why the hell they only had one analog stick on it. The Playstation 1 had already had the Dual Shock out. It was becoming increasingly obvious that having two analogs would often be important for proper camera and movement control, yet they never capitalized on that. Granted, bitching about the Dreamcast controllers could be a whole thread in and of itself.