Pros
Everything was dependent on your division and group: some groups, such as the group run by Dennis Guzik, were fantastic. Others were where retired military went to work til they died, and constantly churned through young engineers. I was never bored, had a plethora of interesting and diverse work, all while acquiring a sizable technical skill-set and management experience. There were many very talented yet very supportive people who helped make me who I am today. HQ was a nice place to work - however, working at a client's site means you can't take advantage of the amenities.
Cons
Left as the company was about to be sold - I've never seen an acquisition of that type that went well in the end. The way it all went about felt very under-the-table as well. Could and should have been dealt with far better. See Pros - while my group/overall experience was challenging but reasonably rewarding, most of the junior technical people I knew at SPA were not happy. There is also a lot of carrying other that goes on in projects. Generally you'll have a couple at the same time, so learn quickly which PMs and employees you like working with, and request to be on their projects constantly. I didn't receive a single non-cola raise while working here. When I left after a few years, my next employer's offer was ~70% more than my total compensation at SPA.