Pros
Friendly atmosphere with smart colleagues. We were encouraged to talk to people face to face. People were busy but were also happy to explain projects in detail. Projects themselves were very interesting. They provide on-the-job training, from theoretical to applied knowledge. Heirarchy felt pretty flat: there's not much room for egos when everyone's wearing lots of hats.
Cons
Very lean staffing. It meant we always felt as if we were reacting and were on the back foot. Crises would be resolved only to reappear because nobody had time to archive and write-up investigations. Onslaught of e-mails. Some of the stress was avoidable at my level by opting not to have a company phone. But there were a few late nights doing urgent analyses.