Reaper is just as susceptible to Boom, Headshot! as anyone but...it's a robot? It can also swim with no trouble and apparently automatically heal damage.
The healing bit is explained in the in-game wiki actually. Apparently, all ground based unmanned weapons by 2065 use self-repairing smart material in their armour that grants them a limited ability to "heal" from damage; Reaper, being an advanced prototype, has a superior version of this. The swimming bit is likely a result of of said prototype status as well; Reaper is probably fairly lightweight and likely has some sort of ballast tank inside of it to give it buoyancy. The head shot thing is probably just for balance reasons.
Maybe that's where his (its?) processor is. A computer can't function with its processor destroyed, what more a robot?
Yeah but that leads to the question of "Why does the super-advanced combat robot play Cranial Processing Unit straight but all the other mass-production robots in the game avert it?"
PerhapsSuper Prototype still means "prototype" and, while he features amazing advancements, they still have some design flaws in other areas?
Or perhaps his chassis is already full. After all, he has to store all that ammo for his minigun arm somewhere and he doesn't have a visible ammo backpack, not to mention being an advanced prototype designed to support special forces units in the field means he probably has an oversized power unit. Add in the above mentioned air bladder for underwater use and his chassis is probably full. Not to mention that Cranial Processing Unit isn't as bad an idea as its detractors make it out to be; after all, soldiers are trained to aim for centre mass and a head can easily be removed and placed on a new body if the original is destroyed.
The writing goofs when you're playing as the female protagonist. The storyline is clearly biased towards the male, with Ship Tease between the Player and Kane regardless of gender, and occasional moments where the Player is referred to as "he". This is because you are reliving the memories of John Taylor's previous mission, who was decidedly male and was in a relationship with Kane.
There are two separate sections in the game where the level's current antagonist takes control of G.I.U. robots and survives, despite Diaz telling you that doing so will fry your brain due to G.I.Us operating via a collective hive. Since Diaz and Taylor are both connected to and controlled by Corvus, a Hive Mind, it stands to reason that they should be able to control G.I.Us without incident.
By the end, John Taylor would have lost quite literally everyone he ever knew throughout the campaign. That is, Hendricks, Kane, Diaz, Maretti, Hall and the Player. One can only wonder what his plan is after the end.
Technically speaking, only the Player and Hendricks actually died- Kane, Diaz, Maretti, Hall were just playing out the parts of JT's former crew, and are still alive. However, JT is obviously tormented- he felt guilty that half of his crew turned traitor for legitimate reasons and he had to gun them down, and was afraid he'd have to gun down Hendricks for being a good man in a dirty situation. After the events of the first and last level, all of his former friends are dead and he's directly and indirectly responsible. This is probably why he tries to save the Player, and the entirety of the plot is his personal guilt trip.
The fact that the entire game is a modified Write Who You Know retelling of Taylor's previous mission, however, only further spells out that this guy who seems fairly well off might just be the worst kind of Stepford Smiler, after witnessing his entire previous team get horribly killed one-by-one in circumstances that likely had something similar to but not quite the Corvus incident. Which effectively means you're reliving the necessary murders of Taylor's comrades Through the Eyes of Madness.
Speaking of which, the Winslow Accord has been dealt a serious blow in the form of the Warzone Zürich ended up being, not to mention the deaths of Sebastian Krueger, and several ZRF soldiers. Worse, if anyone finds Kane's body, then the CIA's Nova-6 production could be revealed to the world.
Even worse, the WA could blame this attack on the CDP, considering how little they know about Jacob Hendricks and his brainwashing by Corvus. This could lead to a World War 3 or a World War Whatever
As said in the Nightmare Fuel page, the robot grunts don't seem to be able to act of their own free will, meaning that somebody explicitly programmed them to rip somebody's limbs off.
Ascended Fridge Horror: According to the Wikia entry on the NRC, "the NRC's technicians programmed their Grunt robots to viciously and methodically assault enemies. When given the opportunity, NRC Grunts were known to capture enemy human soldiers and brutally dismember them before killing them to create an element of fear among opponents." This would mean that the Player is far from the first soldier to fall victim to this.
For example, Sarah Hall was stated to be cybernetically augmented after sustaining injuries in an NRC attack in Egypt in 2060 according to her wikia entry. What if she was a victim of such thing ?
"the NRC's technicians programmed their Grunt robots to viciously and methodically assault enemies. When given the opportunity, NRC Grunts were known to capture enemy human soldiers and brutally dismember them before killing them to create an element of fear among opponents." This would mean that the Player is far from the first soldier to fall victim to this.