Game-Breaker: Both Plasma Pistols, but the Light pistol in particular, due to dealing heavy damage, having a large clip size, oh, and it's available after the first main mission. Also a case of Bribing Your Way to Victory since it's a piece of DLC bonus content. Though it is slightly balanced out by its relatively low ammo pool.
Plot Hole: Reconnecting the infiltrator into Mosaic to learn the position of the Outsiders' mothership reveals the XCOM base to them as well. Said infiltrator had been walking inside the base before Carter joined in disguise as a researcher, linked to the Mosaic all the time until Carter apprehended it. How come the aliens didn't elect to blow the XCOM right away?
Because they had larger concerns - it was only after learning that the other Ethereal was in the base that the aliens attacked in force.
Porting Disaster: If you're on PC and don't have an Nvidia graphic cards, expect the game to barely run better than a slideshow.
Ironically, when The Bureau was revealed, some gamers complained about the removal of investigation aspects and alteration of enemies to make it more like Enemy Unknown.
The Woobie: Bureau Agent Ennis Cole, who's the star of several of the videos. Cole's wife Ann and son Kevin are victims of an alien attack on Pima, New Mexico, and were either killed or infected by the Sleepwalker virus and put down. Cole has a Heroic B.S.O.D., and is scrambled for a mission before he can submit his resignation. He ends up walking into an alien ambush. The last thing heard on the radio is a single gunshot.