The Xbox version may be a slight improvement in some ways, but it has a few minors problems to make up for it.
Unfortunately, even though it's good to hear Ryo's original English voice-actor, most of the NPC voices are very off-putting, and although the major characters such as Joy, Ren, Wong and Shenhua are not bad, some of the rest are just terrible.
Other noticeable features added to the Xbox version are some such as the ability to take an in-game snapshot which can be viewed on the main menu and to change camera filters. Of course, one of the biggest differences from to Dreamcast to the Xbox is the fact that those 4 disks are now on 1 disk... which helps. Of course, almost everything else remains the same.
However, some of more necessary things that should've been tweaked such as the fiddly movement of Ryo seems to have been ignored, and the slightly annoying viewing mode (that sometimes focuses on an object that you don't want it to) seems to be untweaked and ignored aswell.
Fortunately, Shenmue II still keeps it's original story and almost everything else seems to be left the same, so it's always worth checking out if you happened to miss the 2nd installment on the Dreamcast, or if you're just eager to get a taste of the Shenmue spirit. However, if you own the original Shenmue II on the Dreamcast, this isn't really a major essential and is only really good for it's couple of changes or as a collector's item.