Pros
Professional growth is the main reason to join a company like Deloitte. With the amount of trainings and varied on-the-job experience, it makes Deloitte truly a great place to grow. Promotions are pretty straight forward: If you work hard and get recognized for it, you'll get promoted (2 years until Senior, 4-5 years until Manager). There are very few jobs out there that give you this experience to see different companies and understand how they run their businesses. Especially for young professionals coming straight out of college, it's rare to find a position that will grant you this much responsibility at that age. Overall, this is a great place to start your career.
Cons
Work-life balance can be a joke at times as Managers have been known to pressure people to work during their vacation time. Also, you will meet your fair amount of social inept people. The hours worked REALLY vary based on your clients. I know some people who work insane hours while others are coasting their way through. Working long hours does not necessarily mean you will be recognized for them all either. In this age of accounting/consulting competition among the big firms, companies offering services to clients are in a constant battle to cut their budgets to sell their work. This ends up hurting people at the lower levels who have to complete the same amount of work originally planned but in less time just so we can make ourselves more financially competitive. I have heard stories of Managers / Sr. Managers asking their staff to "eat hours" (i.e. not report total hours work) just so they don't have to increase the costs of the engagement. As I stated before, Deloitte is a great place to start your career. This is not to say it's the best place to stay though. I've seen many Managers depressed from the time it has taken away from their family life. Keep in mind that when you start a job like this, you'll potentially have to travel a good amount.