The area that Threespot needs to improve on, is having a unified vision for the direction of the company that is communicated clearly to staff and then managed in alignment with that direction. There are often mixed messages as the company tries to optimize various measures like billability, profitability, timelines, staff resourcing etc. This is a struggle for every agency, but in particular at Threespot, the messaging often created confusion among the staff and then was either abandoned or simply never followed up on. This doesn't really affect staff at a more junior level, but as you advance in your career and are accountable for more than just your deliverables, this can be frustrating.
Threespot is a great employer for people who have had agency experience and don't want to deal with the annoying parts of agencies anymore. It helps to have perspective on what the limitations of agencies are before you work there. In my history, staff that hadn't had agency experience had a harder time understanding why things were the way they were in some cases.