Happy to work for one of the most mature startup companies in Silicon Valley
Pros
Apple is a large company, but often has a small company feel. Most project teams are very small - a few people at the most. Often there are only one or two key engineers directly responsible for features or key project areas. Because of how small teams are, it makes it very easy to approach key players and influence product direction. Conversely, key engineers don't have much bureaucracy to cut through to implement innovative new ideas. It is because of this culture of innovation, as well as a culture of excellence, that working at Apple has been one of the best experiences of my professional career.
Cons
Because of the small business mindset, and the decentralized nature of the decision making and product direction, Apple at times lacks the structure that other companies have set up. There are very few departments that are isolated from their customers - so the process and structure that each group attempts to establish can be heavily influenced or even ignored by those who need to use a back door method of getting work done. It is possible that project managers may pressure engineers or other staff to complete work faster than their managers agreed upon, where in larger companies this behavior would be frowned upon, or forbidden. Some structure is necessary to keep a happy medium, and at times Apple could use more structure.