There is
always a tank mission in the WW2 CoD's... Modern Warfare in my opinion was the most stunning--graphics and story-wise--emotive, cinematic rollercoaster ride i've ever been on. Gears 2 was close, but the story just lets it down in a few places (i would have liked a stealth mission heading into the citadel, because the cover system would work well for stealth play, but instead stupid Dom just wanted to KILL EM ALL in the name of love).
i liked COD4 also because it was completely different to the others in the way that it was more relevant to today's world tensions (as opposed to mindless AI Nazi's getting mowed down ..AGAIN.. in this day and age? Puh-lease.), and the online play simply rocks. i think WaW's focus on realism is detracted from by having a single russian tank obliterate an entire force of german tiger tanks....but that's not the worst thing Treyarch did, i think the worst thing they did in WaW (other than that damn tacky Papyrus font in the menus!!!) was put the same freakin tanks in the multiplayer game.
Instead of shoving you in a tank, COD4 sets you up alongside a tank..which is cooler as long as you don't try to rush forward and get yourself blown apart by 160 mms of explosive awesomeness.
The Zombie-Nazi's minigame was fun though, i must admit, even though it was just a tad ridiculous at the end with a constant stream of the buggers filling every room of the place and slowing the frame-rate down on the ps3 :O what an insult to an awesome system. it still felt like GoW-2's Horde gametype, but the buying weapons part was refreshingly different
In conclusion, i think a tank mission is a bad idea folks

If modern Warfare 2 is released, they should stick to the ways Modern Warfare 1. Make a little change: keep it the same.
P.S. sorry i just wrote a book about modern warfare 1 and World at War in a Modern Warfare 2 thread, but within it i did express my opinion on the topic of this proposed sequel
