Folks ESPP are almost always fantastic deals. Although ESPP do vary by company. My ex-companies was a 15% on the lowest price at the start or end of a 6 month period (the same as Marquette's wife) which is a better than RDamiens. But even RDamiens is a good benefit.
Lets run through some number suppose the stock is $40 less $15% = $34
If you make $68K and contribute 10% for the ESPP that means you've contributed $3400 per 6 month period for 100 share@$40 meaning you've made a minimum $600 profit. But you've contributed the $3400 over a 6 month period, so the return on your last paycheck is fantastic. When we ran the numbers the IRR was equivalent to a 90% return a year for ESPP with purchases every 6 months. And that is worse case if the stock goes up it is better than that.
I'd also recommend keeping the stock for the 2 year period in order to take advantage of the favorable capital gain rate. If you hold the stock for 2 years from the start of the grant date everything including the 15% discount is treated as capital gains. (See Fairmark
) Although others disagree.
My strategy at Intel was to keep 2 years of ESPP and then sell them to take advantage of the capital treatment. If you are contributing 10% of your salary you are holding 20% of your salary in company stock. If your net work is 2x or great than your salary this isn't a huge risk.
In fact if you work for a Megacorp it is possible to buy an 18 month put (leap) for roughly 10% the price of stock, this allows you to lock in your profit while holding the stock long enough to get favorable tax treatment.
Buying a long term put would probably be best in a situation like RDamiens.