jb, do the instructors give you a full brief before each exercise, and what outcomes are expected, sort of like you giving a briefing to your FO before an actual flight? Also, do the instructors talk at all during the particular maneuver, giving hints or warnings about such and such, or even stop it and say this or that needs addressing and start again? OR...is it more like this is the exercise, I will watch you and FO and afterwards have a debrief?
It depends on what the exercise is for. On a training course, they'll discuss exactly what you will be given, and expect to see, and then in the sim will talk you through things as necessary. They can freeze the sim, or instantly jump back to points, if needed to emphasise anything.
Cyclic exercises (the renewals) will generally have a quiz beforehand. There's likely to be discussion items, which normally relate to what will be seen in the sim exercise (for instance ECAM management with multiple faults, and loss of air data, for the volcano exercises). Any new company stuff (standing orders) might be brought up too.
The exercise normally consists of modules some of which might be checks, and others training. Normally there won't be any discussion during the check components, until the instructor declares them complete (and ok or not). Training modules may have commentary inserted at any time, but they'll take care not to interrupt the flow of the events.
LOFT modules are simulated line flights, and they are run in real time, with no instructor input. They end whenever you get the aircraft on the ground, having dealt with whatever issues occurred. The recent exercise ended with us diverting to Muscat, but others have gone to Al Ain, Abu Dhabi, Dubai World. Some have had plenty of fuel when it finished...others haven't. Some have declared emergencies, whilst others manage to find some runway without fuss. You all start with the same basic weather and event scenario, and fuel, but what you do with it afterwards is up to you. Any faults, even if accidentally inserted by the sim (i.e. the instructor forgot to remove something, or sometimes the sim itself just screws up) are dealt with as if they are real.