An almost-excellent film let down by little details

Rating: 8/10 (23 June 2013)

*Spoilers*
The film has an excellent premise and is presented in a very slick documentary style. The acting from Wikus and Christopher is outstanding and the director does an excellent job of making the audience care for the characters. Wikus's characterisation is also very interesting as he is selfish, impulsive and flawed which was quite realistic and refreshing.
There are a few issues in my opinion:

The overly-cold MNU executives were kind of cheesy and too "evil" to be taken seriously.

Some of the CGI Prawns at the start of the movie didn't look too great (understandable with the budget), but of course, overall the CGI is excellent (especially Christopher).

The "population control" scene where they burn down a shack full of Prawn eggs was again overly evil and difficult to take seriously. It can also be interpreted as a heavy handed and out of place comment on abortion, but perhaps I am looking too far into it.

In general, the apartheid allegory seems pretty heavy handed and would have been more effective if it were more subtle (e.g. at the end of the film, Koobus refers to Wikus as a "half-breed piece of s**t,".

When Wikus is ill at his birthday party and says "let's cut some cake," there is the cheesiest, cliché echo sound-effect used in cartoons when a character is dizzy (hard to describe).

These may seem like little details, but collectively they do drag the film down a bit. But there is only one real issue that is outright inexcusable:

They never explain how the ~500ml of fuel that Christopher has spent 20 years collecting is able to power a massive space ship AS WELL AS cause Wikus to transform into a Prawn. Were the Prawns originally humans and did this fuel turn them into Prawns? I mean, that's the only thing you can really draw from that as its what happens in the movie. Is the fuel able to transform any organism into a Prawn?

Also, how can there still be enough fuel after about 20ml at least was sprayed over Wikus's face?

How could they not offer some explanation? This will irritate me for ever as it really drags down what would otherwise have been a fantastic film.