How do I gauge the value of stock options that I have
been offered?
Most metrics are generally useful for tax purposes and tax purposes only until the company IPO's and 6-12 months (or longer) later you can cash out your options the company's stock has no market value.
Will you work at the company for the full vesting cycle? Will you tolerate the culture that long? Will the company still exist in 4 years? Will the company even IPO? How long _until_ the company IPO's?
These are all risks. Most purely emotional. So your evaluation must also be based on emotion.