Creator Killer: The main games, in true Call of Duty fashion, were astoundingly successful. However, the Play Station Vita-based Gaiden Game, COD: Black Ops Declassified, was so bad that it pushed its developer out of console/handheld game development completely.
The Other Darrin: Hudson is voiced by Michael Keaton instead of Ed Harris. It's very noticeable as the two sound nothing like each other. In Declassified Hudson is at least voiced by a voice actor trying to pull off a reasonable Ed Harris impersonation.
Technology Marches On: Averted and played straight early in the campaign. We see Menendez posting a YouTube video in 2021 with the black-and-white video layout that YouTube wouldn't release until a few days after the game released, but the YouTube video still has a top comments feature. Of course, with the rate at which YouTube changes its layouts, it's extremely unlikely that YouTube will look the same in 2021, if it's even still around by then.
Apparently there were plans in place to include a playable female character in the game, with the implication being that the player could choose to go through the game as the son or daughter of Alex Mason. The idea was ultimately scrapped though due to the need for double voice and mocap performance (which, to be fair, would be extensive for the game's main character). Treyarch later went through with the concept in Call of Duty: Black Ops 3.