While I prefer the gameplay of the sequel, I prefer the music and art style of the original. It was just so fresh at the time! When JSRF released, it didn't feel as fresh. It was still amazing, but didn't excite me like the first game did.
I feel that JSR has a much simpler color palate too. Lots of primary and secondary colors. The sequel felt more neon and pastel in the color choices.
Anyway, like Max noted, the game is short and is even SHORTER if you are a pro. I'll admit, I'm not getting JET on every stage, but having played the original six plus times (at least three times with the US version, twice with the JP version and once with the PAL version) I can really blow through this game. Since I know the areas where its hardest to avoid cops, I hit those spots first, so that when the heavy artillery is brought in I only have the easy to tag spots to hit.
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Oh! And something that always confused me about the game: In Benton, specifically the area in Benton Boogie, there is this bit:
http://www.youtube.com/watch?v=SeCRDvwAu0c#t=1m57sWhere you enter the door, go around the corner and get to the top of the building. What baffles me is that just by going up a few steps and turning a corner, you're suddenly four stories up on a roof! Is this a little programming cheat, where you are actually teleported from the ground floor to the rooftop? Really, try it out, it defies space and time. I really think it is a cheat where you get sent to the roof instantly. It's so seamless though. That's why it always blew my mind.