I liked the film.
There were, however, some SERIOUS story problems.
Spoilers to follow:
• The Prawns fuel ...ALSO changes DNA in creatures who are exposed to it to match theirs? ... Really?
(nevermind that I think the "exposed to substance/changes DNA --> body transforms into new form" thing is tired and things simply don't happen that way... do they?)
• Ok, so: "the liquid" (fuel/DNA changing agent) comes from Prawn technology... which all arrived on the mothership with them... but they wait until they are moved from their ship and their technology is scattered in earthbound junkyards before gathering it up to fill a Prawn gascan (as opposed to just gathering the fuel from their technology aboard their ship?) and refuel the command module.. which fell why? and all it took to restore the command module to its place on the mothership was some fuel?
Sooooo... why did it fall in the first place?
• Christopher and his one friend and his son are the ONLY Prawns out of 1.8 million interested in gathering up enough fuel to go home? Really?
• Ok, so Prawns have Superguns. But they let Earthlings cut into their ship, and move them down to the ghetto.
a) Why did they not defend themselves in the mothership?
b) How did the weapons (and other Prawn tech) get down to earth in the hands of the Prawns? If they were being moved, did the Earthling handlers not notice the bazooka-sized gun Prawns were carrying?
c) Ignoring a and b, they are in the ghetto, with superguns, trading them to Nigerians for catfood ... why not just TAKE the catfood from the Nigerians at gunpoint? Or, instead of being treated poorly by South African Earthlings, set up a perimeter with their superguns and.. bah. Nevermind.
I think they could have done a better job on the script coming up with plausible reasons why the mothership stopped, was inoperable, was fixable after a period of time; and why/how the Prawn ended up in a refugee camp even though the race has superior weaponry and sufficient numbers to defend themselves against ill treatment.
Maybe, for example, a ruling class and working class? Or, the ship was a slave hauler and the slaves revolted and managed to trap the slavers in a small area, creating a standoff? (slavers can't leave the area — which happens to be the kitchen/pantry, slaves can't get in, slaves begin starving so they allow themselves to be offloaded to Earth?)
Then the slavers start sending small sorties down to earth in an attempt to regain the "keys" to the mothership from the earthbound slaves in the ghetto? (as a plot device to introduce the alien weaponry the filmmakers obviously want to be included in the film).
Chris, with captured weaponry from a sortie they overcome, now has the means to enter the blockaded section of the ship (maybe the slavers are now about starved out?) to take the ship home?
Yea, maybe needs some work — but I came up with this off the cuff.
My point is, come up with PLAUSIBLE storylines and you end up with a better film.
But I did enjoy it. I hope they do come up with a decent sequel.