Pros
Huge learning opportunities thanks to working in completely different projects. Opportunity to work in different teams and meet a lot of people. Teaches you how the corporate world works and the business world (relations, deals, conversations between companies and higher management...). High standards that push you to work for good results; you learn to deliver good quality.
Cons
Not only based on meritocracy, relations matter a lot. At a 'pyramid' company with such a big base, the speed of growth is low and very dependent on your aggressiveness to push for a promotion (as in real life). There are a lot of not interesting, grey and terrible projects and you have to learn to avoid them - or be lucky enough to have a mentor that protects you from them. When Accenture is not selling projects you probably will have periods when you don't have work to do, and that damages your 'chargeability score'. When that score goes below a certain amount they can fire you - but actually that takes a long time to go below that amount.