The process runs through several levels: First introduction interview, then longer lasting traits and role play interviews. The 2nd interview was 1 h the third one was planned for 1.5 h. Questions were around your past behaviour at specific situations at work ("Tell me about a time you received feedback and how this changed your work...").
At every step you get a good input and tons of material to prepare. The recruiters are very helpful and really want to support you. But, overall, I believe the process is very artificial. All conversations including the 3rd interview (role play) were done "only" with HR and recruiting stuff, that follow a very formal process. They take notes about your answers and later, for example after the role play, give you feedback about your answers. The role play follows a certain structure that is defined and that can be prepared, according to the briefing provided. It is not an open conversation, but a go-through of a previously defined structure. The recruiter wants to hear you asking the right (and a lot of) questions. And you must find out about the real problems of your counterpart.
I don't believe such a highly structured, artificial and unrealistic conversation will help Gartner to find the best salesperson, but the best actor will most likely survive.
Furthermore the process is very time intensive, it needs a lot of preparation and you feel like in university exams. And of course, every longer lasting process will rise the possibility you will finally have a bad day and miss it to ask the decisive, intelligent, killing questions... what I believe happened to me. In case I will be asked by Gartner for new opportunities (what they offered) I will step back from this process - I'm not brave enough, never again.