Pros
At AECOM you do get exposed to a lot of great, world-renowned projects. Graduates are often thrown in the deep end, which I personally found great. Compensation is also quite good. In the UK at least, the social culture is excellent - I have spoken to a few ex-colleagues who reminisce fondly on the social aspect of working at AECOM, and have not found the grass greener on the other side in that area once moving on. In my team, the work-life balance is superb.
Cons
As might be expected at such a large company which often buys other companies, there are many inefficiencies. I.T. is under-staffed and under-resourced. There also seem to be poor communication channels between the technical workers (engineers, architects, consultants) and the finance staff (PCC, Project Managers). Also, staff are often last to hear major announcements about the company's plans.