I don't have an iPhone 4 to compare with right now, but in indoor office lighting, my new iPod Touch Retina display looks washed out/noticeably less crisp than the AMOLED display on my HTC Incredible.
When I previously compared the Incredible to the iPhone 4 display, I was impressed with the iPhone 4 display's crispness, so I am a bit disappointed with the iPod Touch display.
No big deal though, it's still a very nice device and complements my Android phone well. I always liked running two OSs: Windows and Mac at home, and now Android and iOS on the go.