As would be expected from any 100-year old company and a Fortune 30 company to boot, it can be very large and bureaucratic. The nature of the industry as well lends itself to far slower business cycles and a pace of company change that at times seems almost glacial. But within that spectrum, different sites at Boeing can offer vastly different ranges of excitement and change. A lot of it depends on what site you end up working at.
As mentioned before, they have a problem with the development and retention of talented younger people, though they seem to be able to draw them in initially without too much of a problem. But I think, especially for Millennials, the slower pace of the company can sometimes be frustrating. The company also has a more old-fashioned view of promotions, generally adhering to fairly strict timelines for allowing level/grade increases at your job, regardless of how well you are able to do your job. The tendency also to favor older employees who've "put in their time" over younger employees who might actually have demonstrated that they are more capable is maddening at times.