The First 15 Minutes of Rez (Dreamcast)

Copied from MobyGames:

Rez is a fast-action shooter that takes you deep into the world’s computer network. The “Project K” Network has recently been upgraded to handle the rapid expansion of the information age and the core, known as “Eden,” holds the most advanced artificial intelligence the world has ever seen. Unfortunately, Eden cannot handle the ability to create her own thoughts and buckles under the pressure of an existential breakdown. She is lost deep inside the system, and you’re the only one that can bring her back online, saving the world from utter chaos.

You must blast complex viruses, unlock passwords, and destroy firewall bosses as you search for Eden. Each stage is in a constant state of flux dependent on your shooting techniques, which ultimately control the music and colors of your environment. The deeper you get into the dreamlike cyber world of Rez, your form will evolve or devolve depending on your progress.