Avantages
The company pulls in lot of interesting projects and has many high-profile clients. You'll regularly see the company's work in newspapers and on TV. If you earn the trust of the PMs and Principals who work on these projects, you will learn alot. The benefits are above average - 4% 401k match, 3.75% separate retirement account (referred to as a "pension," but it really isn't), and subsidized health insurance. RE is a considered one of the better consultancies in the industry and will be a good addition to your resume.
Inconvénients
Despite your progress professionally, it will be very difficult at the Associate Consultant level to be promoted. In fact, it seems that the business model is dependent on paying Associates lower salaries, even if the Associate has technical and management skills on par or better than existing PMs. High profit margins + high billable multipliers (paying Associates about 25% of the hourly billable rate) + low Associate salary = massive bonuses, for Principals and PMs. This is why the PMs and Principals never leave and there is high Associate turnover. Make sure you negotiate for a high starting salary since you'll likely never receive a decent raise. You'll be constantly told that RE is the best environmental consultancy via self-congratulatory presentations and from management during interviews and conversations. Don't fall for the sales talk - RE is a good technical firm, but there are many others that are just as good, if not better, technically.