LEDs generate a lot of heat in the fixture. It will be important for LED's efficiency to be even higher than today's commercially available ones so that consumers can use them in regular sockets. Today's models need big heat sinks that are expensive and odd looking.
Spectral characteristics and diffusivity could be better as well. LEDs by nature only generate a single narrow band of color. Most people like broad spectrum white light which is a combination of all the colors.
So right now LEDs are good at a narrow range of lighting uses. That will expand, but it takes a while. Organic LED (OLED) technology is an interesting direction that some of the research has taken.