Pros
1.) Employees are very knowledgeable and company is outstanding technically. 2.) Company as a whole is very supportive of personal growth via conferences, internal and external training, and professional organizations. 3.) Health-care and other benefits are excellent. 4.) Many staff interact very well on a personal level. Very good place to meet people who you can be friends with outside of work.
Cons
1.) The biggest downside is definitely the hours. I have worked at other engineering consulting firms before and since and none of them work their people the way Geosyntec does. Working 10-11 hour days every weekday is the bare minimum and when big projects come in the door, easily expect to work 70-80 hours for weeks or months on end. My personal "record" was on the order of 105 billable hours in a week and most staff would give you a number somewhere in the 90-110 range. 2.) Salaries are not terrible, but nothing special. Definitely not commensurate with the level of time put in. In my experience and discussions with others, you can absolutely get similar pay for fewer hours at other firms (or conversely, higher pay for similar hours if that's your preference). 3.) Company does not treat junior and mid-level staff well. When issues arise, junior and mid-level staff consistently take the brunt of the blame while seniors generally skate by. Since the employees are knowledgeable (and they know it), the culture often immediately turns into blame-shifting and scapegoating lower levels.