You are shown an overview map of the target and briefed on your pre-determined waypoints, which you cannot change. Known enemy locations are shown for you, although almost every target also has roaming patrols that aren't shown but are mentioned. If other friendly units will be used, you will see their insertion points and what their orders are. Some background information is also provided about how this mission fits into the larger campaign goals. Once you have read the briefing and selected your kit, it's time to kill.
Missions seem to be scripted, at least at the very beginning.
If repeat a mission, you will see the same guards in the same places, at least until unsuppressed combat is initiated or you are detected. I've seen a variety of enemy responses on the same mission. If you die during the mission, your character doesn't, for whatever reason. Although my main player has been through most of the missions and has died fairly frequently, his kill board doesn't reflect that. While there are certainly advantages to this, it negates any 3D accelerator board that a user may have.