[Magin]

Having seen the film myself, I thought it was pretty good (then again, I'm generally a sucker for Disney)... but I suspect that the reason why it did so poor is because

Spoiler for film:

the war that you see in the trailers is pretty much over by the time Carter arrives, and things don't pick back up again until well over halfway through the film, almost close to the end. The majority of the film is about Carter's journey across Mars, rather than being involved in the war.

... and I still need to find a copy, either in print or in electronic, of the series.