The only real short coming for me was the lack of any real challenge
I always thought a lot of the challenges to unlock the secret characters were tough. I remember spending quite a while unlocking Zero Beat and the Immortals. Still never unlocked everyone. Maybe I just suck.
Personally, I didn't have too much trouble with that. Every time I've beaten the game, I made sure that I collected all the graffiti souls and unlock all the characters in the process lol
But I was talking more no actual threats. In the original game, they had it where the cops would show up when you keep tagging up the level. The more you did it, the more aggressive they got, like, bringing in tanks and attack helicopters and shit. It was pretty tough sometimes, especially while you were trying to complete objectives against the timer. In Future, they reduced the cop battles to these small scripted segments that pop up a handful of times and they're incredibly easy. Even the battles with rival gangs are super easy. The only real thing you have to worry about is falling off a cliff/into water too many times trying to perform a trick (especially in the skyscraper district) and even then it takes a while for that to kill you depending on the character.
I think that the reduced cops and easier tagging was purposefully done since Future focuses less on arcade style gameplay and more on platforming.When I first played the game, I hated that they simplified the tagging so much. It took a while for me to realize that the tagging mechanics of the first game wouldn't work in Future.
The original game was big on platforming too. Even though there are lots of things that I like about Future over the original, there are some step backs too that I wish could have been handled better.
Speaking of the relation with the first game, JSRF always bugged me with how it fit in with the original. It's less of a traditional sequel and more of a re-imagining of the first game with sequel elements (It's set in the future, the characters are older, that kind of stuff). ---