At least five of the Borg drones are Klingons, If Resistance Was Futile for them, what chance would the rest of us have?
The montage in which we see the Enterprise crew failing to hold back the Borg, during which we see several officers are being assimilated. One looking in horror as his amputated arm gets fitted with a cybernetic claw. Another with a freshly gouged eye being covered with an eyepiece.
The entire opening. We see Picard flashing back his time on the Borg Ship and assimilation (Eye Scream included). It's frighteningly disturbing seeing him plugged in to one of those rechargers with this completely emotionless expression on his face, and at this point he's still in uniform and hasn't even had any implants put in yet. And then these flashbacks finish and we cut to present day Picard looking upset after recalling all these traumatic events. Then he goes up and looks at himself in a mirror, and BOOM! - a Borg drill pops out of his face. Yes it turns out It Was All A Dream. It doesn't make things any less freaky to watch.
Dear god, the Borg were bad enough in the TV series, but anytime they showed up in this one the movie actually turned from a sci-fi film into a damn horror flick. One of the scariest scenes is where a handful of crewmen flee inside a darkened room on the ship... and then several Borg lights start flickering on within the room. It gets so bad that anytime we transition to Riker's party talking with Cochrane down on Earth it actually comes off as a welcome breather.
The warp coolant that dissolves (and seems to vaporize) tissue on contact. It's inexplicably kept in gaseous form in an easily-breakable vessel in main engineering.
To be fair, it's easily-breakable by Data, who has been shown to have Super Strength.
Data with half his human skin melted off rising out of the coolant to grab the Borg Queen and pull her down.
The blank looks and thoughtless eyes on the crewmembers' faces when they're in the early stages of assimilation - they're not afraid anymore...
The one crewman who begs Picard to help him as the assimilation process begins. It makes it so much worse when you realize these are probably his last conscious thoughts and feelings before his mind is superseded by the Collective.
That killing him before he was assimilated qualified as "helping" was just as bad.
The way Picard acts, as the situation becomes more bleak by the minute. We're talking a man who normally is fairly cool in most situations, even life or death ones normally. Right from the get go, we see just how personal this is, when Picard is once again faced with the lack of trust of some other Star Fleet Officers due to his time as Locutus (the first being DS9 when Sisko was not all that happy to see him after the Battle of Wolf 359.) Let's put that in perspective. Picard is Captain of Starfleet's newest, and most advanced ship at the time, an Assault Cruiser type ship. And the first thing Starfleet does is tell Picard and crew to take a hike, and DO NOT play the role of being Big Damn Heroes. Obviously Picard is not happy to be reminded of the fact that he had Starfleet secrets taken by the Borg when he was assimilated. By mid movie, he's clearly shifting into Blood Knight territory, taking actions just for the sake of engaging the Borg in battle, including dumping an entire Thompson machine gun's drum magazine worth of .45 calibur bullets into some drones, even after they're dead. Near the end he's crossing into full blown Revenge Before Reason, throwing one of the most violent fits ever seen in a Star Trek series, insulting his most trusted officers along the way. This is a movie which begins to really call into question Picard's psychological health.