Pros
the only reason one would work at Aecom is because of acquisition of another company. Often you can find good and competent people working there. In the initial months of the merger one can also feel like about working in a 50,000+ employees company...
Cons
At least for architecture, there is no interest at all in developing the business line. All the senior management are under qualified individuals with degrees in horticulture(that is the head of pdd the UAE) and no architectural training at all. There is no recognition of good employee, and you can only advance if you kiss up to management, or if you are under qualified. If you are an Architect that cares about the profession or design STAY AWAY from AECOM... In my 20+ years of professional career AECOM has been the worst company I ever worked for.Consider cleaning toilets before thinking about working at AECOM