His claim to fame is his work on the cult hit Fighting Game series, Guilty Gear, in which he produced the artwork, wrote the story, and provided its godly soundtracks. Oh, and he also provided the voice for its lead character (and Ishiwatari's Author Avatar), Sol Badguy, as well as his past self, Order-Sol (except in Story Modes, drama CDs, and Guilty Gear 2: Overture; as of Xrd, the switch to Joji Nakata seems to be permanent, as Ishiwatari indicated in an interview that Accent Core Plus would probably be his last time voicing the character). As anyone who's looked at the character list or their respective moves knows, it's evident that he is a major rock enthusiast. His favorite band is Queen.
With production rights to the Guilty Gear franchise temporarily lost to Sega due to the Sega/Sammy merger, Arc System Works went on to create a spiritual successor in the form of BlazBlue, where Ishiwatari merely produced the soundtrack. He also provided the voice of Freed in Battle Fantasia, another Arc System Works project.
He also provided the soundtrack to Hard Corps: Uprising, and it is still every bit as eargasmic as the aforementioned soundtracks, if not more so.
An often-peddled myth is that he worked for SNK, and was one of the main designers and programmers for The Last Blade series (due to a designer credited as "Daisuke"). However, Ishiwatari-san was already working for Arc System works as a designer on Exector by 1995.
With the recent news of the rights to Guilty Gear being returned, Daisuke finally announced that he was working on a new Guilty Gear game, Guilty Gear Xrd -SIGN-.