Dead or Alive 2 Millennium is an updated version of the Arcade release of Dead or Alive 2, this update made Survival and Tag Battle available from the start and added school uniforms for Kasumi and Ayane, that's it.

Compared to the console version of the game there isn't any reason to play Millennium or the original Dead or Alive 2 on Arcade, I guess it's fun as a novelty but it just has less content than any of the console versions, Millennium only released one month before the Dreamcast release so it's existence is a bit odd, not sure these small changes really mattered to manufactured a whole bunch of new units but what do I know and this has nothing to do with the game itself.

So, don't bother with this! Just go play the Limited Edition Dreamcast version!