"An early review of Call of Duty 4 allegedly leaked in which OXM said the game had a 5 to 6 hour single player campaign when played at normal difficulty. As we've seen already in games like Heavenly Sword, short playtime can get you a bad rep quick. Obviously, COD4 will fall back on expansive multiplayer for added value, but my intent here is not to trash its game length, features, etc.
In the interest of developer-accessible census - what is the sweet spot for a single player campaign length? Personally, I like between 8-12 hours...15 tops. Anything longer and I will absolutely never beat it. Anything shorter and I feel gypped - not for what I paid as much as accomplishment. Ultimately, gameplay always triumphs and exceptions apply. But for your average game, how long should it be?"