ARL is an opportunity for real and interesting science/engineering, just don't expect to get paid very much.
Pros
It is a place where there is an opportunity to do real science in support of our troops and country. I found it easy to get funding for projects that I basically dreamed up. The scientific facilities at ARL are among the best in the world in terms of ballistic and military research.
Cons
The promotional process is very rigid and bureaucratic. This slows career advancement down to an unacceptable pace for many people. The starting salaries are generally well below private industry. Sure ARL and the Feds in general give nice benefits, but the salary is often so low for young employees that it is not competitive with private industry. Wait until you can come in as a high level engineer to work for ARL. Those salaries are more comparable to private industry.