Pros
The Greenhouse approach is truly unique in the marketing and branding world -- work is thoroughly researched and strategy based, refined through a collaborative process that brings the best ideas to the top. The work environment is extremely positive - everyone's input is valued across the firm, and problem-solving is done with a focus on finding a solution rather than finger-pointing. The firm's flat structure allows anyone to take a leadership role. Rather than getting caught up in hierarchy, the Greenhouse way believes great ideas can come from anyone, and that reporting to the work is far more effective than reporting to a boss. Having worked at companies in the past where these values weren't prioritized, to work at a firm where they are has helped immeasurably with my career growth. The results speak for themselves, as the firm has developed long-term client relationships with many national brands.
Cons
I wouldn't call this a downside, per se, but as a smaller firm, Greenhouse emphasizes a close-knit, collaborative environment where colleagues treat each other as they would their own family. I love this aspect of life at Greenhouse, but someone who is used to more impersonal, large office environments should be prepared for a different approach.