As much as I like the sound of the improvements they have made I just can't bring myself to pay $60 for another 5 hour CoD campaign. I haven't bought MW3 yet either for the same reasons.
Until they lengthen the singleplayer I will be waiting for $20 sales on these games, which given their popularity means waiting a long time.
Hell, my beef with this series isn't even the 5 hour length, it's the fact that there is absolutely zero replay value or any reasons to replay the games again once you are done
Take vanquish for example, a game without any multiplayer that can be completed in 6 hours however the thing here is that the replay value in that game is astounding, you always keep coming back for more, whether it's the insane difficulties, the addictive leaderboards or the huge ammount of hidden extras in the game, on top of that, it's the best TPS released this generation.
the SP in the COD games really is like the developer throwing the dog a bone "here, here's your SP campaign, now I'm going back to work on what the most of the people who play these games care about, MP"