That it is, but more than that... how could I put it... the whole purpose of the movie is to show two kids suffering to death. And you know that it ends like that since the beginning. There's no message to speak of (and no, I'm not counting the "wars are bad" thing, we all know that, come on...), it's not by any means an emotional movie, just a depressing one. It didn't even make me cry, and I'm a crybaby when it comes to fiction. It did make me feel sick to my stomach though. So yeah, that's why I find it despicable.
On topic, animes that made me cry... almost all of them? I cry easily, but oddly enough I don't tend to cry to the scenes most people do, so there's that...
And as for the ones that made me cry a lot, well, there's almost every key anime adaptation ever, sure, Clannad, LB, Air, Kanon, Planetarian... Plastic Memories that @Huang Ling Yin mentioned also hit me hard, even though you knew it was gonna happen, and I feel like it's an anime that it's often unfairly criticized too hardly. I thought it was overall good, and really great when it had to shine.
And, for the sake of citing a so far unmentioned one, let's go with Rainbow. It didn't made me cry so hard as the others, but it was probably a lot more depressing overall. Hey, but in contrast with Hotaru no haka, you can find meaning in it.