Finished the campaign in about 6 - 8 hours. It wasn't very difficult at all compared to the other COD's. I would say just a little bit harder than MW2. I would like to specify 3 specific parts of the campaign that you are bound to get stuck on one.
1. First Part: (Executive Order) The toughest part is where you come in and to the right is this office space. (End of Mission) Then you have to make it down this corridor that reminds me of the Mission in No Fighting In War Room. Then you make a left to the door that ends the mission. This part was DEFINITELY the hardest in the game. Tips for that part:
First things first, come around the corner and chuck 2 grenades into the office space. Quickly go into prone. There will be some guy to your right, blast him. Crawl left and keep crawling. Pop up right and shoot 1 - 5 enemies around the bend of this stove you are crawling behind. Gaze left and dive underneath this other rectangular structure. Pop up here and there to take out the rest of the enemies in the room. Listen to what your AI say. Typically during that part they might shoot out something like "Behind the Table." That indicates that you look in the back of the room and there is some guy hiding beneath a table, simple.
The second part of this section is a bit more difficult. Now you will see a lengthy corridor. Take out all enemies within about 10 yards. Then throw a flashbang into the room. On the left side, there is a box run behind there and prone. Take out the nearest enemies then move up behind some kind of small vehicle. Again, take out. There is a small opening in the wall to your left. Take more out. Advance. To your right is a room, in front of you is a hallway. Look right into the room and take out 1 - 2 guys and then sprint into the room. Go to the end and prone. A few guys have shottys, so stay back a bit and pick your shots. Clear the room. You now have corridor and office done. You might get a checkpoint now. Take out 1 - 4 enemies behind some more vehicles. The rest is cake, but take your time if you didn't get a checkpoint. Once you are at the door at the end of the hallway the mission is over. THIS PART IS AS DIFFICULT ON HARDENED. Follow those steps and you got that part out of the way, probably the hardest part.
Rebirth Tank: Round the corner to the right. Grenade launch the two vehicles, then switch to the turrets to take out the guy out. The turret guy will down you about 40 % of your health, but no worries. Now, you will have 4 -6 seconds that your health will be regenerating. While doing so start your aim at the guy in the corner left on a little balcony. After hes done, switch right and take out the RPG's and additional enemies/trucks. For the rest of the way, zoom in and nade the from one side to another. You'll get a checkpoint once you exit the tank.
THE BARREL ONE IS EASY JUST KNIFE THE BARRELS AND BE PATIENT!
That part took me a half an hour to complete, and the tank took me 5 min. I found some videos that could help you through it. Here are videos for each of them, they are not mine. The first video is the one with knocking the two barrels down the hill, the second one is the tank sequence on Rebirth, the 13th mission. VOTE POSITIVE, COMMENT IF YOU HAVE ANY QUESTIONS. YOU CAN ALSO MESSAGE ME FOR ANY QUESTIONS WITH THE VETERAN CAMPAIGN, I WILL HELP! THANKS!