Well, as for the helmet, it comes out of the back of the armor - it doesn't nestle itself painfully at the back of the wearer's neck. The armor is probably powered armor, meaning there are powered artificial ligaments in the back help to lift the folded piece, when in storage (as well as the other heavy bits of the armor; which might incorporate knee ligaments for Isaac's otherwise human-powered legs). And then a robotic limb lifts the the helmet up (there's like one cut scene where I saw this; it's near the end of the game where Isaac is leaning against the wall, and then he stands up... rest is spoilers), so that it can fold over the wearer's head and face (and then provide a tight seal and oxygen, somehow - maybe there's many small carbon nano-tube melded tubes traveling up to the face, woven into the bottom layer (the head covering that Isaac wears underneath the helmet), or something).
The same hand-wave most likely applies to iron man 2. Despite this, it doesn't really explain why Isaac sounds like a deep sea diver whenever he speaks, but whatever.
The plates protect the head, kind of like banded mail or the roman legionaire's breast armor. Each plate folds over the other to provide greater integrity - rather than functioning as one piece, each plate defuses force to help to cushion impact. The plates are also hard, to protect against scratches and dents of slashing or stabbing weapons.
About jetpacks...
Isaac's rocket boots don't accelerate all that quickly. At most, it's maybe 30km/h (and if that's too much, then tone it down a bit more). Really, all he needs is enough to dodge giant hunks of space debris flying towards him. If it feels like he's free falling at the time, then that's obviously style over substance (although zero-g does offer the constant feeling of free fall), but I digress...
Basically, the same technology is used in NASA's astronaught suits, repair of the ISS. Just little puffs of low ejection mass. Enough to maneuver in zero-G.
Isaac also uses magnetic boots to adhere and walk on any surface in zero g. This probably requires a good deal of balance on the part of the user (lift your leg and a ligament in your suit's knee pulls a tiny lever to deactivate the magnetic field in that section of the boot). Whether or not the magnetic adhere-to-anything-not-just-ferrous-metal part is realistic, feel free to argue that, though.
We all know the main reason Isaac is a super hero space marine though is that powered armor is cool and still not nearly main stream enough. xD
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Most of Yatzhee's complaints seem like nitpicks in this one, dating back from his previous review of the game. I thought that despite Isaac's voice, he did seem to be somewhat of a unique character based on what he does in the situation at hand (he's not a wisecracker, but that technically would confine him to a wisecracker formula, ie. - instead, he seems to be just a normal tough guy with the simple title of 'engineer' for lack of a more futuristic job title, that tends to ask questions ("I don't even know what you want! What are you, even?!" was sort of his complaint, a similar thing that Yatzhee wonders for why the ghost girl is more important than everyone else that died on Ishimura in Dead Space 1; you can bet that Isaac would wonder the same thing, if the game wanted to give us extensive accounts of Isaac monologuing) and only proceeds for the sake of his own survival) - compared to most others in the genre.
Watching Toby do a lets play for about 50+ episodes of this game, I'd probably give it a 7.5/10 (.5 because I'm a pussy, screw you).
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What if Max Paine had ended with him shown in an asylum recovering from a Valkyr addiction, the doctors commenting on the fact that he can't tell the difference between his high induced hallucinations and the real murders he committed, maybe even implying that he may have been the one killing his own family. Wouldn't that have made a better game?
I would probably find that incredibly irritating and then blog (and/or spam the nearest chat channel of online game of your choice) about how the story writers were complete ruttin hacks.
IMO, uncertainty is a nice way to tell a story - so long as it doesn't piss readers off so that they can start calling things 'plot holes'. Then you're doing it wrong, no matter what your justification is ("I read a post online about uncertainty!").