'How I Live Now' -- Tween Fluff Or Something Deeper?

It looks like so much teen yearning and struggling to grow into adulthood. The subject, though, demands more. How can you have a tween romance kinda-thriller sort-of drama that involves a nuclear device being detonated over a major city, London no less?

Trailer appears a tad superficial, soft. Flick may be edgy, even searing but I'm not getting it from this.

This review at least supports that a movie can be both, in which case I applaud director Kevin MacDonald and writers Jeremy Brock and Tony Grisoni. Chris Bumbray writes:

For the first forty-five minutes, Kevin Macdonald's adaptation of the Meg Rosoff young adult novel feels like another TWILIGHT. 

Followed by:

But then something really weird happens. After the nuclear attack on London, HOW I LIVE NOW suddenly switches gears and becomes a hard-core, R-rated war movie. 

Really? "Hard-core, R-rated war movie?" That, I'd like to see. Fair enough, though.

Would it frighten the core audience too much if they released a trailer that reflected the change from teen romance to gritty war movie? Maybe. However, this won't have a Twilight draw and it won't appeal to older audiences unless we see something more substantial in trailers. In other words, if we don't get some footage that takes the gloves off, 'How I Live Now' won't have a "core audience".

Update: Just learned this is rated R. So then, the trailers appeal to no one? People who will want to see the movie (not counting the hard-core war stuff) can't because they're not old enough, and those old enough to appreciate such a storyline won't go because the trailers appeal to kids.

Is that it? Did I get it right? Sheesh...