I don't have a ton of experience with the DQ series. I played the original on NES, and bought VIII and played through roughly 25% of it. I enjoy them quite a bit. Definitely old school mechanics, and it's a series that really doesn't take itself nearly as seriously as the Final Fantasy remakes.
I have never played the originals, but I can say that the remakes on DS are well done. The graphics are very pretty. I can't compare the content to the original, so I'm really not aware of what (if any) significant changes that were made, but I'm currently playing through IV and having a blast. I have yet to open V though. I figure since IV, V, and VI are meant as a trilogy there's little point until I finish IV. V is getting very difficult to find, as apparently it did not sell well in the states. I was lucky enough to find a copy on Newegg at the end of last year.
IX is supposed to be a pretty significant departure though. Famitsu gave it a 40/40, for what that's worth.