I understand a lot of the reasons listed in some of the 1/10 reviews...

Rating: 6/10 (28 December 2018)

..The viewers are left to 'fill in' the glaring holes and loose ends by their own, most notably why and how the Police and FBI's ineptitude is beyond repair..
A few unlikely reasons could be:
* The following media circus influenced high ranking officials to consider this a 'case closed'
* Rosamund Pike's character's rich parents influenced high ranking officials to consider this a 'case closed'
Both of the above combined with that 'Gone Girl' (the movie, not the character) maybe deliberately makes a parody of the majority of investigators - except 'Rhonda Boney' who knows the "victim" is a liar - high profile media coverage and the juidicial system.
A political comment about farcical media 'for the masses' and corruption. Dark satire of sorts. If you will.
Previous 1/10 reviews I found good were the ones pointing to the numerous plot errors, I'll just add to a few previous points:
* She bought that cheap car for her disappearance with cash to avoid a transaction trail, you'd assume she'd further already have fake IDs/licences/car registered in a phony name, etc. in order to avoid being traced - further assuming her fake alias(es) would check out when scrutinized
* The monitor camera for the sex/murder scene could be either turned off or there was no camera for that angle/bedroom
* You might assume she could have deleted any camera recordings that disprove kidnapping and abuse - if she had access
* The Neil Patrick Harris character wouldn't have an alibi for the duration of the "kidnapping" and 'Amy' wouldn't be recognized by anyone when they were seen together, even that guy who remarked she looked familiar and none of the neighbours noticed her leaving the house alone during the "kidnapping" (most unlikely)
(Might give this a rewatch in case some details are wrong, in that case an edit will follow)
Movie suspension of disbelief fanfare and then some. She'd be caught and convicted, hands down. But hey, Ben Affleck's character ended up with those sweet deals in the end, pointed out by his top priced lawyer.
So it's all good?
Implausible plot especially towards the end qualify for a 1/10 on its own. But seen as dark comedy disguised as thriller.. Overall 6/10, nice production. Affleck, Pike and supporting cast did alright.