Pros
The culture among teams is usually particularly cohesive and enjoyable. As with any company, particularly large ones, I'm sure there are particular groups with less than desirable culture, but those I deal with regularly are good. As a growing company, there are a lot of career growth opportunities. This extends to people with particular combinations of hard and soft skills having the ability to create brand new positions based on what they bring to the table.
Cons
As with any consulting firm, when jobs are underbid, it is the people that actually do the work who suffer, even though they had no say in the project pricing and promises. I believe ICF should spend more investing in enterprise infrastructure and skill growth. The most common reason I see for turnover is stress from having too much to do but no time to invest in upping staff skills or building the appropriate tool set to stop requiring that each new project reinvent all of the wheels.