Ventajas
Lots of flexibility in job requirements. Over the dozen or so years I have been here, I have pretty much written my own job description. Small side projects became larger projects, become job requirements. I have not had a manager give me 'an assignment' in the last 8-9 years. It is a very self-directed environment. All the creature comforts are here: free drinks, breakfasts, Summer Outings, Anniversary cruises, etc... All the benefits that matter are here: 401k match, insurance plans, profit sharing. Respectable salary Being a worker-bee with no eye towards management, I am quite happy to do the 9-5, and not think about work at all when I am gone.
Desventajas
There is not a lot of promotions here. That said, I think people come in with weird expectations: It is not high school, you don't get a promotion every year. Realistically, every position I have held here had possibility of being a life long career position. If there are only five levels to each job, and I could be here for 40 years (a real possibility!), exactly how fast do you expect to move through the ranks?