It definitely lives up to its antiquated reputation - your dry cleaning bill will be high and your salary will be uncompetitively low. (Note salaries stay largely the same across the country, so while those at Peterbilt in Denton make good money for the area, those of us in Seattle really don't.) Promotions seem to be more based on time of service (and at higher levels, having an MBA) than on aptitude; once you have the basic level expected, doing more does not seem to be rewarded.
The company is quite inflexible, with even seemingly small things requiring multiple levels of approval. This bureaucratic culture stifles innovation and can be frustrating at times.
If you like WFH, then steer clear - we are 100% back in the office with only the narrowest of exceptions. Low-level employees can apply to work from home one day a week (only Tues, Wed, or Thurs, of course), but there is a very limited quota for this, new employees are not eligible, and every single application requires executive-level approval. It's as ridiculous as it sounds and it is widely unpopular.
The company is trying to improve in terms of diversity, with new councils promoting various diversity initiatives, usually themed events with diversity-related swag. It's a start, but leadership is almost all white and male and the culture reflects that.
Pretty much every office across the company is quite spartan, with more luxurious ones featuring amenities like free coffee and a lack of asbestos. Definitely cannot compare to the quality of life at most other large companies in the Seattle area.
PACCAR is big on locking you in. Pretty much every program or opportunity you'd want to try carries a minimum commitment to stay with the company afterward. A master's degree or MBA is necessary to advance; the company will pay for 50% of it, but then you've got a minimum service commitment. Also, by moving you around so many departments, the only thing you'll end up being an expert at is PACCAR itself, which makes you an uncompetitive candidate elsewhere. Many people stay at PACCAR even when they don't like it because they're locked in or because they find they don't have the skills to earn a more competitive salary elsewhere, and end up quite jaded about the company.
Finally, the whims of upper management and the C-suite carry quite a bit of weight, resulting in rather anodyne rules like never being able to put your suit jacket on your chair. (It's the Chairman's pet peeve, you know!) It definitely has a bit of an old boys' club feeling to it, and not in a good way. Stories abound - I heard that the CEO got mustard on his tie at one of the divisions and had them renovate the whole cafeteria to prevent it from happening again. That is hearsay, but it doesn't sound ridiculous when you come to know how PACCAR works, and that should be telling.