As I said the other day on Twitter, I'd like to see a class system like that of Neverwinter Nights combined with a war sim in the vein of Call of Duty: Modern Warfare.
In Neverwinter Nights, each class represented a unique playstyle. Despite having very few dynamics in story and combat scenarios, I replayed that game many times just to play around with the classes. Based on D&D rules, the game let players choose which skills to invest in each level, as well as character aptitudes and other customizations. Ultimately, the player's character was unique within a class as much as because of that class.
First-person war sims tend to either fixate on one class of character or have the player constantly changing class. An example of the latter is Sniper Elite. An example of the former is Modern Warfare, in which each level starts the player in a different role and the player is usually able to switch weapons during the level.
My suggestion is to make the player pick a class of soldier at the beginning of the game, stick to that class and develop it throughout the campaign, and then replay the entire campaign as different classes. So the player might go through the entire campaign first as a sniper, then replay as commando or engineer.
Levels could be tackled from any angle, but the difficulty of each level would depend on the player's class and choices. So a scenario that was easy the first time through could be difficult the next time through. The other option is to make it an open world game. That's rare for war sims, but I'm not sure there's anything that makes it more difficult than for other genres. In any case, such a game would have to have more dynamics in setting and story than Neverwinter Nights had.
I'm not saying this is a better way than normal war games. I'm just suggesting it as a fun possibility. What do you think?