OK, note that this entire post is full of spoilers.
Now, i haven't read the comics, so people who have can probably answer a lot of things.
Firstly, the entire scene at the beginning where Simon rescues River absolutely rocked. I was really happy about seeing exactly how he managed to extract her in the first place, and we finally get to see it.
Simon has really developed, i was surpised he'd stand up to Mal and then later actually floor him! I guess living out in the black for a while has hardened him. He even takes a swig of the booze Jayne slides across to him. For some reason Mal no longer considers him one of his crew like he did at the end of Safe, was this change covered by the comics?
If i mainly talk about the things i thought weren't quite right, that's because i saw it as a great movie with off parts rather than a bad movie with ok parts.
It got slow in the middle, and i thought it was going to pick up when River attacked Jayne and Simon, but i think it got a bit aimless until they dress up Serenity as a Reaver ship. When they got onto Miranda the whole suspense and mystery thing seemed sort of angsty, and the trippy spinning-around camerawork gave me a headache.
It didn't really have any happy bits in it, in the series you got to see what Mal and the crew were like when they were mellow or just getting on with chores or whatever, but everything in Serenity was serious/passionate/pathos-ish with a few jokes sprinkled in. (But i have to admit Kaylee's complaining that for ages she hasn't 'had anything twix her nethers that doesn't need batteries' was hilarious).
The big space battle was great, we finally see what space battle looks like in the Firefly-verse, with missiles and tracer fire everywhere and Reavers being fond of grappling or tearing apart ships. Although it would've been nice to get a bigger view of what was going on rather than all the claustrophobic close-ups.
I didn't really feel the fact that Zoe was hiding her pain about Wash's death under her military training, so her little out-of-control vengeance spree seemed somehow hollow.
How could Mal hold his own against the Operative in the final showdown? I can understand if he was being toyed with in the scene in Inara's room, with the Operative's Morpheus-esque "What do you think you're going to accomplish here" (or something like that). But being a uber-assassin i really would have thought Mal would get dead in a few seconds in the serious showdown.
The door being only able to be closed from the outside and the big computer rig sitting above a Pit-O-Doom seemed a bit contrived. Also the way Serenity got dramatically smashed to bits then at the end it's all put back together seemed a bit 'reset buttony'.
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More technical stuff:
Judging by the point-flashes on Earth's surface, the economic strife of Earth 'being used up' led to a nuclear world war.
The Firefly-verse now definitely takes place in one system, that just happens to have a huge number of bodies. "Dozens of planets and hundreds of moons", means there's probably a lower limit of 224 and upper limit of 1095 (96+999) planets and moons in the system.
I can't remember, so does anyone else know if we see the Firefly sun in the opening space scene? I think it might have been yellow, which puts a limit on how big the system's habitability zone is.
Was the planet Inara was on Sihnon? And was Book back at the monastery on Persephone?
Why exactly did they have to go through that big collection of Reaver ships to get to Miranda? Was that really the easiest way in, so they couldn't go around? It's a bit confusing.
Also, why didn't the Reavers land on and pillage Miranda?
When they mention Miranda has normal everything including gravity, it made me wonder- how is Firefly terraforming supposed to change the gravity of planets and moons?
Why wasn't the Serenity crew affected by The Pax? Why wasn't it still in the air?
I got the impression it's not as realistic as the tv show. E.g. Simon's planar energy-grenade, the new Mule being a typical scifi hovering antigravity vehicle, the cliche-nebula-like Ion Cloud around Mr Universe's planet, the Reaver EMP glowing beam cannon.
It's weird at the end how they're flying through rain, then they're above the clouds, then then fly up a bit and they're already in space. Reminded me of ROTS's sudden 'We're in the atmosphere!'.
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Stuff that wasn't in it:
What ever happened to the 'Hands of Blue' guys? They were nowhere to be seen!
It didn't involve Blue Sun at all, except i saw an ad on Mr Universe's big multi-screen display.
Alliance gunships like the ones seen many times in the series (the fighter-jet-like ships) were absent or not seen visibly.
The Ballad of Serenity, or a variation thereof. At least a reference like "You can't take the sky from me" or something would've been nice.
The Reaver split tongue. Since the proto-Reaver in Bushwacked cut his tongue down the middle to 'make himself look like one', i figured we'd see split Reaver tongues.
I think that for someone who hasn't seen the series, they didn't really make the bilingualism/multiculturalism very clear. I expect a lot of people kept thinking 'I didn't quite catch what that guy just said'. In fact i often found myself thinking that from the sheer denseness of things to see/hear/understand.
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Other musings:
When they're robbing the security firm, i thought i heard the guy say 'Give me your Opposition password' before they spray a volley in reply. Is this Opposition some kind of anti-Alliance organisation like the Rebellion in SW?
Why didn't Mal or Inara kill the Operative with a shot to the head after he was flashbanged by Inara's 'incense'?
Book's past remains a mystery. I mean, did Whedon even
have any future plans about why he wasn't who he seemed? This reminded me of a Red vs Blue PSA where Sarge is briefing them about the upcoming campaign but to any question they ask he just says 'Sorry, that's classified', and at the end Church whispers '...I don't think you know either'.
Where on earth did that weird Uber-Bow thing come from that Inara used on the Reavers coming through the choke point?
Am i the only who saw Book's first name as being Derria? I looked it up later and people were saying it was Derrial, but i could've sworn i read 'Derria'.
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Little things i noticed, trivia, etc:
We see a biography of Mal flash on a screen of the Operative, but i can't remember any of it.
When they first touchdown on Miranda, Jayne is wearing a yellow spacesuit instead of their normal ones, but Mal and Zoe are using the old ones from the series. Perhaps it was a replacement for the one Jayne shot through using Vera in the series?
I don't know if Jayne had this before, but there was a patch on his jacket that looked like a US military rank insignia. When i
looked it up, the closest i found was either USMC Master Gunnery Sergeant, Major Sergeant or Sergeant Major of the Marine Corps (not sure which).
Wrestling moves- in the barfight, Jayne flips a guy upside down, hugs him and slams his head into the ground (i'm sure it has a name). Also at the end Mal pulls off this move where grabs the Operative then dislocates both his shoulders simultaneously.
Those six decoys that shot out of Serenity looked a lot like the scene in TESB where the hyperspace pods zoom out of the ISD in all directions. I guess these would be Cry-Babies #7-13?
That AA gun they bolted onto the roof looked like something straight out of a WWII exhibit, can anyone identify what it was? I had a coolest-shit-ever moment when Mal opened up on that Reaver scapper, it was brilliant.
The box-like cargo section of Serenity nearly came off the rest of the ship in the big crash landing, possibly suggesting that entire part is modular?
Wash's death by 'surprising impalement while still in pilot's chair' reminded me of Trinity's death in Matrix Revolutions.