To me, much of Dragon Quest's music doesn't really stand on its own out of the game. I'd compare Sugiyama to Jeremy Soule in that regard.
In-game it's usually very pleasant to listen to, mood fitting, and whatnot, but most of the time I just can't remember the songs, a few exceptions, of course.
For example, this song literally embodies Dragon Quest VII, despite none of the songs being particularly memorable on their own.http://www.youtube.com/watch?v=SAZfEJpfEYk
For the most part, I find Sugiyama's boss and enemy themes to be drastically lacking, where field and town themes are far superior. The only boss theme I'm really fond of from Dragon Quest is IV's Estark battle, which hits all of the right battle theme notes for me.http://www.youtube.com/watch?v=Rz1LAucsTaM
(It starts at 2:38 here)