One thing I'll say about government work -- you're not really breaking new ground, from a technology perspective. (Unless you're at DARPA I suppose.) Don't come into thinking you're going to innovate in some bleeding-edge area. But government was left so far behind the consumer technology curve that basic, competently-executed, well-designed software that's fast is an _enormous_ leap forward. 2008-era web tech is sorely needed across government. In a way, that is the innovation: dependable software that reliably delivers services to people for whose user-experience has never been put on the same playing field as consumer online services.
If you're interested in being part of the rebel alliance, and for whatever reason USDS or 18F aren't right for you, consider contracting. There's enormous opportunity to make real change and see your code help others. Believe me, small teams can have a big impact on government, even from outside government. If you want to know more about Ad Hoc, get in touch (http://adhocteam.us/). We also have projects with the Department of Veterans Affairs, and state Medicaid programs.
I never thought I'd be a government contractor. I did the startup thing, and just happened to get roped into the HealthCare.gov rescue. I can tell you it's sometimes frustrating, but always satisfying work. And there are several avenues in.