Congratulations on the acceptance. Everyone knows that BCG is the best consulting firm in the world! (I am kidding, I just obviously come from the same firm).
The review process... intersting question. As consultants, we always explain to our clients that they need to focus on just a couple of main KPIs, that you cannot improve everything at once. Yet ironically, this is exactly what we expect from the consultants.
I suspect things change fast, but during my time we had 6 main categories, each broken down in a few more sub-categories. For each of these, we'd get a grade at the end of every project. In other words, there was always something we would get hammered on and absolutely have to improve :)
The actual process isn't very standardized. In my first project,I'd get a review discussion every 2 weeks, with concrete examples to support every point of feedback - both positive and negative. All too often though, the principal on my subsequent projects would only give me my feedback once, a few weeks after the next assignment had started.
The best way for you to improve is to seek feedback if it doesn't come, request actionable feedback with real & fairly current examples, and try very hard to act on that feedback. You should ask your Manager/Principal obviously, but also Partner if available, and even your fellow consultants. I'd also ask the support staff for input, they know more than we sometimes give them credit for.
After a few months/ 1 year, you will probably have the opportunity to select a mentor. Choose wisely, make sure that mentor cares about you and will help you rather than just check a box.
The job is tough, but the company will try hard to make sure you progress fast. If you need help, don't forget to raise your hand.
Good luck - and congrats again!