I've got to say that even though I love all of his books (bar the Jon Shannow novels 'cos I haven't really given them a chance yet.. though I will!) I think the Rigante series was the best. Though, the Troy books were fixing to be his best work. I can only hope his widow can do the last book justice.
BTW - Anyone else feel violated after the terrible ending in Stormrider? After searching desperately for an answer to that horrible last chapter, I discovered DGs' very own complaint and apology (which I can't find the link for so your going to have to trust me on, sorry.) He stressed that his publisher was really riding him and he was already way overdue on his deadline. He also expressed a desire to release a revised edition of the book at some point in the future.
*sigh*