Pros
HDR has grown by acquisition to get the best talent they can. HDR does a little bit of everything, and thus inspires engineers and scientists of many persuasions. HDR has many initiatives in support and development of staff. Corporate values are shared and emphasized with staff.
Cons
While HDR's work is diverse, when you get down to the local level, there are many cliques and silos. Lip service is paid to worksharing and cross-training, but ultimately, whatever benefits the bottom line the best wins the day. This puts short term profit over long term investment in staff and growth in the marketplace. Your experience as an employee is highly dependent on the skill and professionalism of the local managers. Note that engineers (including those in the C-Suite) don't necessarily make the best Executives... especially when an executive has to make business decisions on businesses that are outside his professional experience.