GTRI is a great place to work if you want to work on defense-related R&D-type work. Since it is mostly defense work, you need to be US citizen, and eligible for a security clearance.
You get the opportunity to branch out, beyond whatever you already know. That makes it different from large contractors, from what I hear.
You have a lot of autonomy, whether that means you will have time to explore subjects and solutions you might not have otherwise, or just slack off, will be up to you. However things tend to get more hectic when it is time to deliver, or demo to a customer, etc.
In exchange for greater opportunity for career growth, and more personal autonomy, expect to get paid less than you probably would in the private sector (GTRI is technically part of the state gov't).
GTRI is such a vast institution that no two people have the same experience. They break up their organization by labs, branches, and divisions, so there is so much spread that you often do not know what your neighbor is working on.
In my experience, the on-boarding and HR process is full of "gotchas" when it comes to setting up your work environment/office, PTO, parking, and etc. Communication lacks and people make rash decisions on the daily. For me, that caused me to stress out, because there were many instances of me making a change, then the next day I learned the change was not urgent at all and needs to removed/changed in some way. They describe the experience as "dynamic" and want people that can fit into that model.
The last thing I will mention is that everybody is highly intelligent, which is awesome, but does lead to pride and ego issues when you try to steer their thoughts into a different direction.
I have worked at GTRI for almost 4 years; the first 9 months as a student and then became a full-time researcher. The work environment is very flexible and GTRI offers very interesting challenges to work on.The best part is the entrepreneurial-like experience. Employers are encouraged to seek out their own, that is most interesting to them. This could be through submitting your own proposal or finding projects already within GTRI to contribute to.