Not sure the "startup work environment" of macbook pros and free lunch will really help you compete against startups that offer stock options in a profitable company. Selling people on taking a worse deal in order to make the world a "better place" always seems disingenuous to me whether the goals are altruistic (help the American people!) or commercial (re-invent the tablet!)
If I put on my employee hat for a second, this is what the deal sounds like:
1. Work on uninteresting or incredibly regulation-encumbered projects that can't or won't be measured on customer satisfaction. Where do complaints about healthcare.gov go? How are you as an employee of the contractor that made it able to respond to those complaints? At least when its a product 1) people can go to a competing product (show failure), or 2) people can use it because they genuinely want to (show success) and not because its the only game in town.
2. No potential massive IPO (per the description here).
3. Very unlikely you'll get the actual cool perks of adding quirky features you guys come up with together from analyzing customers. Its probably going to be a super refined spec, decided by a bunch of politicians, and since you're working at the lowest bid anyways even if you could afford to work on cool genuine ideas you have, you probably can't afford it.
4. Huge potential for the project to fail for political reasons anyways. (or you'll have to work with other gov contractors on a different part of the project)
5. The reality that some component of the company will have to become good at the "gov contracting game".