* For most of the campaign you'll use the Hysteria (Leopard), and only get the Argo at the end of part 2, with the Question Of Faith campaign flashpoint.
* All of the original campaign contracts have been modified and the text rewritten according to the new story.
* Several of the new campaign flashpoints have consecutive deployments. This is done to increase the challenge of having to run multiple operations with limited assets, and for story telling proposes, since the story of the flashpoint involves fast operations. Certain flashpoint choices can reduce the number of consecutive deployments or allow you to use third-party 'Mechs.
* The original flashpoints of the five Inner Sphere factions are optional to play during the campaign, and will immediately precede the 4th Succession War. They're also played sequentially, starting from the lowest difficulty.
* On campaign, JumpShip access to the Inner Sphere is limited, and depends on you unlocking letters of marque from the Successor Lords (which also unlock their faction FPs).
* More terrain variety - in the original game each contract (like One Man's Art) can only appear at a certain system difficulty and certain campaign milestones. Those limitations have been removed, allowing for a greater terrain variety during contracts. 
* The special equipment of the Marauder has been nerfed, with the Called Shot ability reduced from a 33% maximum to 25%, and the 10% damage reduction only applying to the Marauder, not the whole lance.
* Stores/Black Markets have been changed to restore the appearance of LosTech to before the HM DLC was released.
* Opfor pilots levels can vary, being possible to encounter pilots with a different skill levels than the contract's difficulty; there's also a chance some of them will be immune to headshots (to balance the Called Shot ability).