As far as I understand, OLED is more similar to LCD than plasma, but it is better in almost every way: cheaper to manufacture, much more energy efficient, brighter, have more vibrant color, doesn't suffer from the viewing angle problems LCD has, contrast ratio on the order of 1,000,000:1 since there is no backlight... black is black, have a faster response time, and are thinner.
It's a pretty impressive and exciting piece of technology. It means a lot for the future of laptop and cell phone battery life, as the backlight of an LCD is a significant power draw.
The only downside is life. The OLED elements can have a lifetime as short as 14,000 hours (compare to 60,000 hours for LCD).