Jet Set Radio
I played this game on the Dreamcast at my friends house. Jet Set Radio (released as Jet Grind Radio here) was a game about rollerblading and tagging graffiti through the streets of Tokyo-to. We would spend hours playing this. The game had a lot going for it, but stood out in the art direction. Jet Set Radio was one of the first cel-shaded games that I played, and I even looking back almost 15 years, it doesn't look that bad.
As you'd expect from a game about graffiti art, the game had a very street feel with crazy vibrant colours. The characters were all done in an anime style, but you could see strong North American influences that bleed into Street culture all over the world. The setting is in a Japanese Metropolis mimicking Tokyo, but I read later that there were a few New York inspired levels.
Most importantly for me, the soundtrack for the game was incredible. The game developers went out of their way to find great musical artists like Mix Master Mike and Jurassic Five, but the two main artists Hideki Naganuma and Deavid Soul really took precedent. To this day, the soundtrack holds as one of the best I've ever heard in a game.
As for the gameplay, there was something very satisfying about nailing a long streak of rail slides and mid-air taggings that no other game has seemed to emulate. Because the game was based on momentum, there'd be times where I'd bump a wall by accident or hit a rail at a slow speed that was very frustrating. This wasn't exactly a game flaw in my eyes, however, as it made landing all the tricks that much more satisfying. It's a shame that most of the Dreamcast games didn't make a big splash in North America, because this game deserved the same recognition as Crazy Taxi.