Pros
You're helping protect wildlife, habitat and endangered species, how awesome is that? There are truly some great people in this agency. Great training facility (NCTC), national scope and ability to travel, some flexibility in schedule. If you're in the right program and position for you, life is good. Job security.
Cons
The USFWS isn't exactly a young, strong, sleek agency. Maybe that was in the 60s-80s with the ESA new, expanding refuges, a strong bent towards technical control of nature with fish hatcheries. It's past middle age, kinda overweight, out of shape, grumpy, not particularly open to change, and trying to find a purpose in life.... ...The ESA, while an amazing law, has become difficult to implement. The refuge system seems dated, industrial hatchery production is a big part of Fisheries, attempts at landscape-scale collaboration was almost universally disliked by leadership and most staff. There is an archetype of the grumpy, introverted wildlife biologist who doesn't like people or change. There is some truth in this, and it plays out often here. The Peter Principle, like in many gov't agencies, plays out often. I've had 3 Supervisors. One was competent and a real professional inspiration. One was the boss from hell, the other just didn't care about much, seemed lost and always gave up. In many cases, one needs to re-locate or take a job they don't want in order to get promoted. Administration change. Certain administrations don't seem to value public service to wildlife and conservation as much as others. It can be a jarring change to how the agency functions or doesn't function. This agency seems conflicted with itself and the future of conservation. Lots of traditional wildlife management types focused on small areas, one species, probably missing the bigger picture. Maddening to try to instigate innovation or change.