let's see, rushing through 1 level in doom or wolfenstein takes about 15-20 minutes.
15-20 levels per episode, doom had 3 episodes (or 4 on the XBLA version) and wolfenstein had 6
15x 15 minutes = almost 4 hours for 1 episode. *3 is 12 hours in a game where the entire game is about the same file size as 1 character is in COD.
now, that is assuming you can even rush through that on anything other than the easiest settings. and as I said, there are enough interesting things that make you WANT to go see the rest of the map.
now, COD. all you do is walk forward. you can occasionaly take a different route but it takes you to the same place as the first route would've brought you. going back through that other route (if you're even allowed to) will get you a few more kills, which add 0 score and gain you absolutely nothing.
I have never taken longer than 6 hours for any COD game, and never on a difficulty setting lower then the 2nd highest. and there was absolutely nothing for me to gain by going back at any given time.
Modern games just completely limit your freedom. they take you by the hand and guide you past movie sets, where all you have to do is point and click. And a lot of people like this. I don't see why, I probably never will. And I really don't care. I just don't like it. Now i'm not gonna say people like me are better, or people like you are. we're just different. But what I can say, is that there is WAY more effort put into the map designs of the games I like than in the scripted fancy explosions in the games you like