Pros
Lockheed offered very exciting work for a co-op. I was an integral part of the test team, even able to travel with the team to missile launches. Very exciting and rewarding work. The engineering work possibilities seem to be numerous. Since I was a co-op, I was not exposed personally to the benefits, but found that most of my regular, full-time co-workers were pleased with what was offered. The traveling I did gave me exposure to the corporate travel policies, which were very good compared to what I have experienced at other companies. Our accommodations were always top notch and the per-diem was very reasonable.
Kontras
HR had way too much control. My senior engineering manager wanted to hire me as a part-timer while I finished my engineering degree, but HR refused to let it go through. The hiring process involves searching an enormous database of resumes for keywords in your resume - no regard given for having already been there as a co-op. Although I spoke to several HR folks at job fairs, who were amazed that I hadn't had an interview, I couldn't get through the politics. Perhaps it's better that I didn't, although it was a very rewarding place to work while I was there.