McKinsey & Co recruited from my college. After being accepted for an interview, I was offered a number of interview prep opportunities - a conference call phone session with other applicants reviewing the process and a case, an in person group case work through with a representative, and a 30 min online Q&A session. We also had to take a written business skills test that is McKinsey-specific the night before the exam for an hour (it seemed easier than the online samples). The first round interview itself was two 45-min separate interviews with a fit scenario (about overcoming challenges, working with difficult people) and a case each. One of my interviewers prodded at my example, asking things like "what did you say?" to get more detail; the other gave much less reaction.

Rigorous but fair questions - mostly case based. Two sets of interviews x 2 rounds. You only get invited back for the afternoon if you pass the morning round. They expect a high degree of mental math and creativity. Worth prepping for standard case interview style questions, using frameworks but able to adapt them.