The original creator Tetsuya Mizuguchi had to get the license back from SEGA in order to issue the Xbox 360 version of the game, even though he created the game at the time. That is because video games created for a company are usually considered "work for hire".
An undocumented feature for the PS2 release of the game is that while you are in the pause menu during gameplay, you can press triangle and square together and the pause menu will disappear allowing you to see the game behind it.
The Dreamcast version is relatively rare today, especially because the game suffered from many defective pressings. The risk of ending up with a non-working copy of the game is therefore something to be considered when prowling eBay or other online auction sites.
On 2003, July 31st, a private REZ event occurred in Tokyo, where the team showed new game content to a few selected people. One of the levels was based on Fat Boy Slim music, but never made it into the game due to licensing reasons.
At the end of the credits, Rez is quoted to be "deciated to the incredible creative soul of Kandinsky".
Abstract artist and composer W. Kandinsky was a synaesthete (a person with the neurological condition in which two or more senses mingle into one), meaning he was able to 'see' music and 'hear' color. He described his works as quoted:
"I applied streaks and blobs of color onto the canvas with a palette knife and I made them sing with all the intensity I could..."
The nature of Rez' audiovisual experience and the referrals to synaesthetia are obviously linked to Kandinsky, as well as the working title, "K-Project".
The Japanese Playstation 2 version was also sold as a limited edition box, bundled with the Trance Vibrator -an additional (external) Rumble Pack whose name left little to be desired of the imagination.
Rez was released on the Dreamcast, months before the PlayStation 2 release took place. It's not widely known that it was never released on the former platform -both SEGA and UGA officially mention the PS2 release only. This is very likely due to the fact that SEGA discontinued the Dreamcast months before the release of Rez.
As a result, there was no American release of Rez on the Dreamcast, and there was no real publicity surrounding the European release either making it a hard-to-find title.