Tokyo Xtreme Racer Zero. As a driving game, it's pretty abysmal; the physics are a joke, Suzuki Cappuccinos and Honda Beats can somehow keep up with a tuned R34 GT-R, and the harder races are usually luck-based. However, there's something magical about this game... It's a very cool "Shuto Expressway Simulator" if that's a thing. Prowling the C1 for street racers to chop (and be chopped by), hitting 250MPH on the Wangan, strategically planning where to pick your battles based on your knowledge of the expressway... It shouldn't be as addicting as it is, yet I've watched many nights turn to mornings because of it.
https://gfycat.com/gifs/detail/SmartCornyDegu
I really want to like Forza Horizon, but when an early PS2 (and originally Dreamcast) game does the open-world car game better, there's a problem.