All the campaign missions are incredibly varied and interesting. The Berlin metro infiltration followed by a cat and mouse chase with the Stasi is insanely well done. Just a chance to see the Berlin wall again is amazing, I have spent around quarter of hour just looking at all the intricate details, then the café scene, finding the infomant and then infiltrating the house of that Soviet spy followed by an incredible warehouse shootout, just fire! Then you got the amazing mainframe retrieval with all the ziplines, bow, stealth etc. But nothing really compares to the KGB HQ mission, which is probably my favorite mission in Call of Duty history. The music, aesthetics, feel, background dialogues, all the rooms you can enter, so many ways to finish the mission followed by a mad dash to the vault and then a re-make of the MW3 finale with the juggernaut suit.
SLAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAMIN'!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! And we haven't even gotten to the dream level, which is honestly the most creative level in Call of Duty history. It totally gave me the Jacob's Ladder vibes if you do the mission in a certain way and you get the zombie fight in the caves which is insane if you don't know it is coming! Sorry if you didn't know about it but that will stay with me for a LONG time, holy shit. And how the names change from green to red if you decide to lie is an amazing little detail. And finally you got the final mission of which the Tula is way more interesting and fun. Shooting all your "buddies" is not something you usually do, no more "friendly fire will not be tolerated"