Pros
Bain is a highly successful firm, so firstly, the opportunities to gain professional business experience are second-to-none. Personal development is a priority, so you learn a lot quickly - and training is awesome (and fun). It is a truly global firm, and from the get-go, there are opportunities to build friendships with friends globally - and you will, since Bainies are very diverse but in unity a 'friendly bunch'. Even as employees 'at the bottom of the hierarchy', you're made to feel personally valuable. This reflects in the flexibility, opportunities and work. The superlatives continue elsewhere too (amazing offices, events, perks, tech, externships, flexible promotion, transfers (especially) etc.)
Cons
Everyone at the firm is exceptional and the work is often stressful. always demanding. Naturally it's constantly challenging to keep at the pace. It can feel perhaps too cliquey at times. Travel can be rough (though you're generally treated well) - although probably less so than at big competitors due to an office-driven staffing model. This does mean that you'll likely have a mostly random experience of cases though - ACs have little influence over what cases they're assigned to, and inevitably some 'lose out'.
