Ventajas
Deloitte is pretty prestigious as a consulting firm, and the opportunities for growth here are great. You can learn a lot from the different projects, and you'll have the opportunity to work with a lot of brilliant people. The culture at Deloitte is phenomenal - there are very few people at the firm that are unlikable, and those that are tend to leave pretty soon. The company has many events (social, philanthropic, etc) to encourage you to build your network, and while you may feel like you spend all your time doing firm activities, they're fun and enjoyable, so you WANT to spend your downtime with your colleagues.
Desventajas
Staffing isn't a very transparent process, and until you've been at the firm for a few years, it's pretty much just luck whether you get on a good project or not. You really have to build a strong network in order to hear about opportunities, and sometimes you just can't get the timing to work out. As with any consulting firm, some projects are long hours doing boring work, and you just have to suck it up and deal with it until you can finish that and move on to a better project. Recognition is also kind of luck of the draw - if you happen to get a counselor that's very well known and respected, you'll do well at year end reviews; if you get someone who does their work but otherwise keeps to themself, it will hurt you at year end. It's all a big game to be sure that you're doing activities that are 'seen' by senior management, and it's frustrating sometimes to put a lot of time into one project, but get little to no recognition, and then put in minimum effort on a project that's high visibility, and be praised for the one that barely required any work. Deloitte likes to think that we're a top-tier firm, but the truth is we're a step below McKinsey, Bain, and BCG. In a few years we may be up there, and in certain areas we're at their level, but for now, we just can't match them, particularly when it comes to strategy projects. Clients tend to hire one of the big three for those and then look to us for implementation work, which isn't nearly as exciting/interesting.