Jet Set Radio isn't as fun as JSR Future, imo. I love the Dreamcast, it's probably one of my favorite consoles ever- but JSR's controls are just... Super janky compared to it's successor, which is different in many ways.
Future takes more of an emphasis on doing tricks and finding secrets, which the original JSR was more about being able to complete levels in time and without getting caught up by the cops. While that was enjoyable, I feel like Future's way of only having certain levels with them makes it way more fun.
It's super easy to get stuck in JSR, but in Future, there's tons of stuff to do until you 100% complete the game, which unlocks new characters and new maps in multiplayer mode. (Which was really fun, even with bots!)
Lots of people say JSRF isn't as challenging, but I disagree. Each map raises the bar more, with more hard platforms to reach, just like the OG. It just takes out some unnecessary, unfun stuff.
That's my take!