I've previously outlined the 3 fundamentally unique characteristics of Glass:
1) Hands free
2) Heads up display
3) Omni-present/friction-free (it's always there)
I think #3 is by far the most profound. As I've outlined before, every new computing platform reduced the friction between the user and the computer. Glass is the next step after smartphones.
Computers are phenomenally good at looking up and displaying information extremely quickly. See Google search as the prominent example. However, translating real world input from a smartphone (or any other existing computing device) in real-time is too troublesome. Who's going to walk around the world holding their phone in their hand? That's where Glass comes into play. Glass provides an incredible new opportunity to compute on an enormous amount of data - a raw audio/video feed of what you're seeing - and display contextual information in real time. There have been myriad augmented reality apps released for smartphones, but most of them have failed to gain any significant traction because there was too much friction between the hardware platform and the user; the software was dead on arrival. Glass creates enormous new opportunities.
The best Glass apps will be those that take advantage of this unique trait. The implications are absolutely incredible. In the not too distant future, you'll be able to contextually pull up information about almost anything in front of you. There will be opportunities in manufacturing, healthcare, education, and a host of other industries.