This guide was recorded on the Hard difficulty setting. There is a unlockable "Black Ops" mode which seems like it would be a more difficult setting, but it is really more of a "cheats" unlockable mode. On Black Ops difficulty, you get the M16A2 as your starting weapon (an M16 assault rifle with a grenade launcher attachment) along with infinite ammo (this includes the grenade ammunition for you rifle). Also, when you pick up any other weapon, like an RPG, you also have infinite ammo for that weapon. In terms of game play, the AI is not any better and the enemies are just as difficult to kill as on Hard and there are no further health pack restrictions. Thus, there is no real value in making a guide on the Black Ops setting for guiding players through the difficult sections on the campaign.
That being said, the game does have several types of secondary objectives that can be completed - the number of and type depending on the difficulty you are playing on. On Hard, you only have to get about half of the secondary objectives to complete the mission and they are all either Recon, Armament, Blackmail, or Intel objectives. On Black Ops, you are required to get all of the objectives plus complete all of a new type called Destruction Objectives.
Therefore, the walkthrough focuses on the Hard difficulty to help you achieve the unlockable Black Ops mode and give you tips and strategies that work for both modes. In addition, the walkthrough picks up all of the secondary objectives for each mission. In addition to the main walkthrough, there is an Intel guide showing the locations of these objectives and a separate Destruction guide showing where all of the destruction objectives are for Black Ops mode.