Pros
Ernst & Young offers great opportunities for development and education as a first job. You work with young people who, for the most part, are a pleasure to be around. The social network you develop is great and as people come and go and your list of clients grows, your network grows to include many places outside of the firm. The firm does a good job with flexibility (especially in the summer), and for the most part I feel like I do have quite a bit more freedom than I would at other jobs. However, this of course depends on the client you're on.
Cons
There are a quite a few downsides of working at Ernst & Young. First, I have found, especially in audit where there's a "CYA" mentality (as there should be), there are many administrative tasks that get quite mundane. There have been too many times to count where I've been instructed to 'roll forward' a checklist from prior year which involves a couple of hours of fun cutting and pasting. Also, while the summer hours are generally great, this is balanced by the fact that there isn't a whole lot of work to do and thus boredom once again creeps in. I find myself wondering if I would like the short hours and nothing much to do like the summer or the longer hours but with days that fly by like busy season. Also, I've heard that benefits (401k, health, etc) aren't great at E&Y - my dad, who has been involved in HR for years at a large corporation, claims that EY's 401K match has got to be one of the worst of any large firm or corporation.