After some deliberation, I bought Soul Calibur today on XBLA. I already have the game on Dreamcast -- not only do they look nearly identical, but the XBLA version is lacking the mission mode! All the museum bits are available from the start, but it seems like a pretty weak port to me. The lack of online play, combined with the decade-old graphics (which were stellar on the DC, especially with VGA) makes this meh at best. SC fans like myself will probably enjoy it, but every one else is advised to wait for SC4 to drop in price. Don't be put off by the 4 either; if it follows the mold of the other games, it will continue to be the most accessible fighting game out there (including SSB).

tl;dr - SC1 is for nostalgia and/or fighting game fans who inexplicably do not own a Dreamcast (does such a thing even exist?). Everyone else is advised to wait for SC4 to drop to their desired price point -- if history is any guide, you won't be waiting too long.