Pros
Market leaders in some very interesting environmental technology. Some very committed and capable people. Lots of highly educated people (PHDs all over the place) who are leaders in their fields of science. Overall the firm is more professional than you'd expect for a company with <1000 employees.
Cons
It's privately held which gives more latitude on short term vs. long term goals but ownership is rather distant and only really cares about cash generated by the business. Senior leadership is rather disfunctional. Not very effective in setting a vision or communicating effectively with each other or the broader company. Bonuses were a joke. Payout system really meant they were hardly ever going to really pay out. Don't believe when they say what the "target" is. Ask them what the history of payout is.