How many hours is this game?
It's an on-rails, arcade-esque game that originally releases in 2000 on Dreamcast. As other users have reported, a playthrough of the main 5 stages takes approximately 60-75 minutes, but the game is designed to be replayable for higher performance gains -- ie higher scores.
Area X is about 15-20 minutes, which was introduced in this version only.
There's a few extra modes like a Boss Rush, or a straight-run mode (combines all 5 stages into a single run rather than selecting them individually, basically a survival mode). There's even a mode that unlocks where you're invincible and can't die, if you're just wanting to play to enjoy the experience -- it's also a good way to practice and learn better play patterns for when you want to shoot for high scores/higher completion rate.
I tend to think that this game and Starfox 64 are kind of the best of the best in terms of "3rd-person on-rails arcade" shooters out there, with Rez being far more distinctive due to its rhythm-based design. The game kind of molds all of your actions into the rhythm of the music, making it feel like almost everything you do is contributing to the experience.
I personally highly recommend it, even at the full $29.99 price tag and if you don't have VR, but especially if you've picked up a PSVR.