In all honesty, CoD1 = 1800Hours play time, CoD2 a little over 2900 hours, CoD4 a little over 110 hours.
CoD2 was just AWESOME. I loved it, it took skill, single shot Bolt Action rifles will never be beaten. I got good at it too, as you would after 2900 hours. I loved that game, everything was brilliant. CoD4.. added some random crap in that took away from the original and LOVED CoD formula, im sure a lot of you love it. But i don't... CoD2 was harder, with better maps and some truly awesome mods.
Ofcourse it runs like a dream now aswell (But i guess CoD4 is playable on most systems).
CoD5 will be a welcome return to WW2 for me. I'm just a bit miffed they seem to be adding perks again..