Finally had time to see this. Quite a good film. The digital cinematography looks a bit rough and digital but you forget about it pretty soon. The minimal budget doesn't really show other than in the digital cinematography and the idea that the enemy is almost never seen (bullets and grenades just start coming out of seemingly nowhere), which however works fine for a jungle war film. This film really shows war at its ugliest: there's nothing pretty or heroic about it. Popular war movies like American Sniper or Fury or Tae Guk Gi: The Brotherhood of War all seem strangely clean and polished in comparison.
I don't think this is necessarily among Tsukamoto's very best films - it's still kind of missing a little bit something in terms of storyline and audio/visual execution - but it doesn't matter. It's a very solid movie and comes recommended. I would personally rank this in the same category as Kotoko, which I also thought was pretty good.
And yes, the film carries a pg-12 rating in Japan. Which is absolutely fucking insane. You get headshots, arms and legs blown off, brains splattered on the ground (and one solder stepping on those brains) and of course cannibalism.
Tsukamoto is very serious about educating youngsters about the horrors of war, though. He's been inviting high school students to the screenings and holding discussion events with them after the movie to discuss the film and its themes.
The film is performing over the expectations, being a bit of a mini-theater* hit. 30 00 admissions in three weeks so far. It seems to be more than they expected for such a non-commercial film which Tsukamoto is distributing by himself. That being said, the (supposedly) nationalistic mainstream war epic The Eternal Zero sold 7 million tickets a year ago, so that's the sad reality out there...
* Japan has this really cool thing called "mini-theater ranking", which excludes all big multiplexes and only includes small theaters. This allows you to see how smaller audience films are performing, which is really good because those films would never be able to enter the national top 10 list (you'd need a very wide distribution for that, and only major studios could do that)
Weekly Mini Theater Ranking (in Japanese):
http://www.kogyotsushin.com/archives/minitheater/
National Weekly Top 10 (in Japanese):
http://www.kogyotsushin.com/archives/weekly/