Vantaggi
As a merchant you will find no better education. I learned so much from Mickey and his teams; he might be the biggest perk of working at 770. That being said, J.Crew is different from any other retailer and it's definitely not for everyone; but if it's for you, it's the best place to work. 770 is an awesome location. Work/life balance exceeds most other NYC-based retailers. The discount is, of course, a huge perk.
Svantaggi
The state of business today means that raises, promotions, and perks are sparse to non-existent. Salaries are at the lower end for the industry. Working for a brand whose image went from top of the industry to the bottom in ~5 years is tough. The office environment can be cliquey and there is definitely a system of favoritism (though this is true for most companies in the industry).