DQ8 had some different aspects, but in most cases technically it was still technically following all of the previous main Dragon Quest games in gameplay, story style, characters, etc. The only differences was the battle system VIEWED differently (but still technically plays exactly the same as the previous incarnations), and the 3d world view, which was always previously seen from a "sky above" viewpoint.
DQ9 for DS is going to be changing a LOT of things for the series, and a LOT of fans were startled at the announcement. Things like real-time fighting and multiplayer have never been implemented into the series before, so we'll have to wait and see how things turn out.
Personally I want Final Fantasy Tactics Advance 2 DS a lot more. :)