MongoDB

The actual work here is very interesting. As a systems engineer, I couldn't ask for much that's more exciting than helping build a database. Peers are very intelligent, and care is put into making committed code as good as it can be. I've learned so much on the job here.

Management is unskilled and untrained.

Some people who work here are jerks, and are allowed to keep being jerks as long as they produce quality code. This drives away other talented, friendlier engineers.

The culture is unhealthy in promoting quality/quantity of work over most else--interpersonal relations, work-life balance, and personal sanity included.

Diversity in age, race, gender, religion, undergraduate college, and many other vectors is sorely lacking. Female employees, especially engineers, are treated unfairly no matter how much MongoDB pays lip service to this cause.

Invest as much time into being a good manager as you do into being a good coder.

Listen to your direct reports when they come to you with concerns, especially interpersonal or career-path concerns. I know too many coworkers who feel like their concerns fall on deaf ears.