Nuketown is probably the most played map. The fact that it's the smallest map is probably not a coincidence.
Firing Range is another popular map — and it's frequently chosen whenever Nuketown isn't available.
Anvilicious: Killing Castro in the first mission (or rather, his double) causes you to get the achievement "Death to Dictators", and the killing shot goes into slow motion while heavenly music plays. It's pretty heavy-handed, especially considering that Castro was a living leader of a modern country (at the time of the game's release, anyway). The Cuban government was not pleased when they found out. They even accused the US of trying to do virtually what they failed to do in Real Life.
Complacent Gaming Syndrome: Treyarch appeased the NUKETOWNNUKETOWNNUKETOWN crowd with a playlist that rotates on that map alone, though it's only available during double-experience weekends on consoles.
Complete Monster: General Nikita Dragovich is a sociopath who creates the "numbers" program that brainwashes captive American soldiers into sleeper agents to kill their own people. Dragovich first demonstrated his untrustworthy and callous nature at Stalingrad, when he deserted his own men and left them to be butchered by the German forces. After the war, Dragovich would lead a project to recover the biochemical Nova 6 weapon. To test its effectiveness, Dragovich and his right-hand-manColonel Lev Krevchenko used it on Russian soldiers, including Dimitri Petrenko. Dragovich would later become one of the Soviet Union's most powerful members, where he would capture Alex Mason and brainwash him into becoming a presidential assassin. Even worse, Dragovich planned to use his sleeper agents to release Nova 6 on the whole of the United States.
Good Bad Bugs: If afflicted by a Nova Gas grenade, the player's character will call out a warning. If they stay in it, they'll call it out again later. Wearing a Tactical Mask makes a player immune to the effects of Nova Gas, thus causing a player using it that decides to stand in the gas whatever reason to be yelling something like "GAS, INCOMING!" to Department of Redundancy Department-levels for their allies to hear and be amused by.
Black Ops is on both sides of this trope. One one side, the final level of World at War has Reznov stating that he and Petrenko will return to Russia as heroes. In Black Ops, they are betrayed by Dragovich. Petrenko gets a brutal Cruel and Unusual Death and Reznov spends the next 18 years locked up in a Hellhole Prison. Also, one of the lyrics in the game's closing theme Won't Back Down is "I'll drink gasoline and eat a lit match". In Black Ops 2, if Karma dies and you spare Menendez, then Menendez will do exactly that.
Happens again with the release of Black Ops 3. At the end of Project Nova, Reznov asks Mason if he can trust his leaders to destroy Nova-6, or if he thinks they will keep it for themselves. Naturally, they keep it, and naturally, a containment failure causes 300,000 deaths in Singapore.
An In-Universe example in the form of a letter in the game. If the player checks the mailbox for Bruce Harris in the terminal, they can read a letter from Harris's wife telling him not to climb the Eiffel Tower due to his fear of heights. In "WMD", falling off a catwalk after it was hit with an RPG is exactly how he dies.
Rewatch Bonus: The little details about Reznov stand out much more on a second playthrough. Why is he continuously going on separate missions with Mason's MACV-SOG unit? Why is he looking healthy and squared away like one of the American Marines, even wearing an American uniform? The answer to the first question is because he's not really there. The answer to the second question is likely because Mason is replacing an actual American on each mission with Reznov in his mind. It would be Foreshadowing, except it's cleverly hidden by Weaver's presence; because Mason describes him as being absolutely trustworthy despite being Russian in a short throwaway line, we assume the unit has some sort of policy that lets defectors serve with them. The first time through, the player assumes it's just a weak excuse to keep Reznov around for more of the game, and since most players like him, it's not even thought of as a problem. Even Reznov's appearance in the tunnel isn't true Foreshadowing, because it's made to look like Mason's buddy is chastising him for being startled, hiding the fact that he's just seen Mason talk to someone who isn't there.
Additionally, Mason's fanatical need to kill Dragovich and the others can easily be explained on a first playthrough by revenge and the fact that he was directly ordered to by John F. Kennedy himself. On a second run, you can see the compulsion programmed in by Reznov.
Lag compensation. This is the game that started it all. With all the misplaced fan complaints about lag ruining their games, Treyarch decided to redo the netcode from the ground up. Unfortunately, the changes they made came with some rather negative effects on the gameplay experience. They added in something that attempted to "equalize" everyone's connection when the game starts, but this made the experience comparable to having a host from across the world. In addition, host advantage, which was virtually unnoticeable in earlier games, became very noticeable due to the changes. Having host was practically a requirement to use killstreaks such as the Chopper Gunner because, more often than not, if you're not the host you won't be able to kill anyone with it.
Respawn point placement — particularly on the Firing Range and Nuketown maps when playing either Capture the Flag or Demolition. Respawn points for each team are restricted to very small portions of these maps, and they rarely have any vertical cover. It's not too difficult for a team of experienced players to trap the other team into a corner, racking up kills as quickly as the other team's players respawn. Making this matter even worse, if the dominant team has a Chopper Gunner overhead and attack dogs on the ground at the same time, players on the weaker team are better off putting their controllers down for the next sixty seconds.
Special Effect Failure: In "U.S.D.D.", there's a brief scene during the meeting with JFK where Mason hallucinates a 1911 pistol in his hand, turning to face him and aiming it at his face before things go back to normal. Much later in the game, when it's glossing over the possibility that Mason really did shoot JFK, rather than reusing that bit of animation... they simply put a still picture of JFK from that cutscene and overlay the 1911's regular in-game animations over it.
Spiritual Licensee: To The Rock.Modern Warfare had already tried their hand at a homage to the movie with its rescue of Price heavily based on Mason's infiltration of Alcatraz. Black Ops, however, is almost a prequel showing Hummel before staging his blackmail attempt, with Hudson voiced by Harris, a deadly chemical weapon serving as a precursor to VX and a character named Mason who had Been There, Shaped History.