Dragon Quest Symphonic Suite Live Best was one of the first few orchestral game music albums I heard, and despite having almost no familiarity with the original music I was blown away. Even as late as Dragon Quest IX, Sugiyama was still composing great music for the series. I never saw him conduct but he did speak on stage at one of the Dragon Quest orchestral concerts I went to. (Qui-Gon Joe, I believe it was the Dragon Quest III concert we went to.)
There's no getting around the fact that some of the social and political beliefs he was deliberately outspoken about have left a glaring red asterisk on his legacy. As for the musical future of the Dragon Quest series, with Dragon Quest XII on the way we should know fairly soon whether it's the last all-Sugiyama soundtrack or whether a new composer will already contribute.
For any orchestral game music fans who haven't heard the series' music, especially those open to a classical bent to orchestral adventure, I highly recommend checking it out. Here's the listing of Dragon Quest soundtracks reviewed here (DQVI Symphonic Suite is the only favorite of mine I've yet to review myself, but the reader reviews for it are spot on) as well as a discussion thread where we talked about the various symphonic suites for the series.