As you mentioned Jet Set Radio inspired a chara for a Futuristic-Fantasy Fighting Gamer game-idea, had loved the style with the bright colors especially the yellows.
Square Enix , Capcom, Midway, SONY, Konami and Rockstar Games are all inspirations since childhood. My current project started as an Action Horror Videogame, so the entire presentation plays off like a videogame on console, right down to loading screen and trophy pop ups.

And yea same, I look at the series that inspire me to keep within their level when it comes to how they make epic presentations and stick within ratings etc
Inspirations for Sick Boy include: Devil May Cry, Castlevania, MGS, Resident Evil, Tekken and Dead Space
Especially love Kojima/MGS Storylines for their wackiness and detail in backstory,
it's something i also enjoy doing, giving characters bizarre powers and situations while grounding it within the rules of the world. Because 'Sick Boy' was a game idea 1st the game original rules heavily impact the outcome of events.