Pros
HNTB was a place where I was very excited to work...initially. The benefits were good. Your manager may be a nice person to work for. Work hours were relatively flexible. Very large, high-profile, and interesting projects.
Cons
It turns out that there is a culture here of BSing forecasts in order to make things look much better than they are. Only HNTB can make a revenue chart that's filled with red bars and tell you they're meeting all their forecasts with a straight face. Additionally, there is a lot of politics going on within individual offices, and between offices. Some groups in the office get light on work, and interoffice work sharing is so restricted, that it just doesn't happen without some sort of formal agreement. There is a ton of gossiping about office leadership and senior managers, and it often sounds more like a soap opera than tales of an engineering company. Many high profile firings and reassignments during my time there. Because of the company culture and lack of honesty and ethics, the turnover at HNTB is huge.