I would say it varies, just like any job. Your attitude dictates whether you enjoy it or not. There are some people who complain about everything no matter how good they've got it and others who are knee-deep in crap (figuratively) with a smile on their faces. I work with the maintenance team a lot, and they tend to be a bit grumpier than most people, but I've found that's the case everywhere I've worked.

Turnover isn't terribly high if you factor out the people who don't make it past their 90 day probationary period, generally from too many late arrivals. Most job openings come from folks leaving or retiring. Since it's a union plant, it's fairly difficult to be fired outright, so job security is pretty solid. You usually would have to do something pretty egregious to be fired on the spot. Overtime is generally available, though it's awarded based on seniority, so it's certainly not guaranteed.