Pros
The founding team and business heads are extremely good at what they do, and the environment offers an immense opportunity for learning. As people, the leadership team are an extremely open and fun bunch! The founders trust their employees, and don't hesitate to cede ownership of projects. As a result, at Walnut, one gets to own and manage business critical projects at a very early stage. As an intern, I co-owned a critical project, and got to see it to fruition, while receiving timely support and advice from the leadership team.
Kontras
The office space may be a little small (they have plans to move to a larger space in a couple of months, I think), and some of the top brass like to keep the AC at 18 degrees. :) Warm people, but cold conditions, haha. No serious cons as such. Thoroughly enjoyed my time at Walnut.