Pros
The company is large so there are lots of jobs posted and the opportunity to move around is there--it's not terribly difficult. The key is networking, which is abundant. Being internal gives you a better idea of the job titles and salary ranges available for various jobs. If you're applying from the outside it's an undecipherable corporate maze. There's lots of groups and internal resources. The company has some nice perks for events and activities in and around NYC. There are lots of JPMC office buildings and each has its own culture. The HQ at 270 Park Ave is super flashy (which some like and some don't) and has a nice employee cafeteria and an internal Starbucks. There are on site nurses, doctors, physical therapists and lots of other services available for employees. The culture of work/life balance and all other such things depends solely on the Line of Business (Commercial Bank, Investment Bank, Asset Management, etc). The Retail Bank is probably a standalone entity that cannot be compared to any of the other lines of business because it is incredibly different and distinct. Most people in Commercial Bank seem to be the happiest and most content with their colleagues even if they don't particularly care for their job. But that's what the internal job referral site is for. Move on! Move up!
Cons
Large corporate maze. Moving around can be hard to do because corporate titles are hard to understand even internally. There are tens or even hundreds of thousands of people in some Lines of Business making it very hard to know what people really do. There are a TON...absolute TON of middle managers. Just managers in charge of other managers who really shouldn't be employed but were moved or shuffled from some other reorganized area and ended up being a manager of managers. Pay is not as high as the competitors like Goldman, but JPMC is so much larger that it wouldn't make economic sense for that to be he case (this doesn't apply to Investment Banking, as that is a different animal).