This game is actually fairly easy to beat on veteran compared to earlier games, especially considering I've beaten Call of Duty 4 and World at War on veteran which are nightmares. No level is really very difficult, and the hardest part I faced in the entire campaign was the last level when you're fighting on top of the train, as it's hard to aim when the screen is shaking the whole time. Some general tips though:
- There's finite enemy spawns in this game, so don't feel the need to run and gun. If you hang back and just pick them off one by one you can win easily.
-The AI in this game is vastly improved compared to other games, so if you're afraid to face combat, let your allies engage in the firefight while you hang back. They usually can manage to kill about 50% of the enemies per engagement, and the rest you can handle.
-Be wary of your allies verbal commands. I can't tell you how many times Hesh has told me "Move up!" just for me to get shot by the enemy hiding behind a crate. Wait a few seconds to ensure everyone is dead before popping out.
-Grenades are the devil. If a grenade lands near you, even if you're being shot at, RETREAT. Find cover further away from the enemies, as grenades will kill you even when you think you're at a safe distance. Your chances of getting shot while retreating to another cover spot are MUCH lower than the chances of that grenade killing you.
-Checkpoints seemed to be a little more sparse than usual, at least I thought, so be wary when engaging and note when you get a checkpoint. The worst is popping your head up and getting killed by the last enemy in a area then losing 10 minutes of progress.
-A very obvious tip, but necessary. Just crouch behind a crate/box/cover and come up to shoot one enemy then crouch back down. That's the basic tactic for veteran. Repeat crouching, standing, shooting, and crouching again.
-And last but certainly not least, if you get shot even once, it is imperative that you prone immediately, and crawl to cover if you're in the open. It take only 2-3 shots to die on veteran and getting hit once puts your that much closer to getting sent back to your last checkpoint. Never get cocky and think "let me try to get just one more enemy before I crouch." Keep your head down.
So that's veteran in a nutshell. Some pretty obvious tips, but just figured I'd share. Good luck!