Pros
Unquestionably on the leading edge of marketing (and using technology/data to do marketing better)...and because of this Kepler teams get to be free to create and innovate in a way that never happens at other agencies or consulting firms. It also results in very rewarding client response. Smart people - very strong group of professionals that don't fit the profile of an agency...very analytical, very smart, very good with clients....more akin to mainline consulting firms (but having more fun). Great culture - a clear priority has been placed on establishing and maintaining a culture where great work get done (and there is still room for fun).
Cons
While it has grown a lot, Kepler is still in the later stages of being startup so there are occasionally startup-like headaches (e.g. desk space is tight, never enough conference rooms, one of the founders is the IT department, etc.).