Since I'm a military history major, I tend to notice an awful lot of the inaccuracies in games. For the most part I can dismiss them, but every once in a while there is a particularly offensive one that just drives me crazy for whatever reason.
A good example would be the new Company of Heroes 2 game. Everything they have shown is about how cold the Soviet Union was. They are making it look like perpetual winter was the only thing that stopped the "God-like" Wehrmacht. That idea was completely dismissed by any actual Eastern Front historians for several decades (Read: David Glantz, David Stahel, Alexander Hill and various others).
I particularly like David Stahel's new works on Operation Barbarossa, which was supposedly this amazing demonstration of the Wehrmacht's perceived awesomeness. He took a serious, in-depth look at it and realized that the German invasion was collapsing well before Winter even occurred. A combination of poor planning, poor kit, poor logistics, lack of strategic direction, deficiencies in the German 'Blitzkrieg', the sheer size of the Soviet Union and the fact that despite the officer purge, the Red Army was fighting back far better than anticipated.
Anyway, my point is that they are waaaay overemphasizing widely held stereotypes of the Red Army and the idea of "General Winter" doing everything for the Soviets, at least in their marketing.
Something minor that will drive me crazy is if they have MG42s, long-barrelled Panzer IVs, Panthers and crap during Operation Barbarossa or whatever. I'm hoping that they will at least have a Panzer III model, idealistically a Panzer II or even some captured Czech tanks. Same with something like the BT series and T-26 for the Soviets.
However, I'm a bit more forgiving of technical stuff like that, since they only have so much time and money to produce a certain number of units. Especially for a game like Company of Heroes, which is all about creating a super-streamlined, relatively fast-moving RTS.