So, for no discernible reason, I ended up seeing Piranha 3D tonight.
The gore effects are the typically, wildly over-the-top stuff you'd expect from Alejandro Aja. Plenty of well-chewed bodies and severed limbs floating in the water and well as some ridiculous shots like two piranha fighting over Jerry O'Connell's floating penis. (In 3D!) The dialogue is as bad as you'd expect, Richard Dreyfuss' cameo is as pointless as you'd expect, Kelly Brook gets as naked as you'd expect... really, for the most part, it delivers most of what you thought you were getting when you walked in the theater.
What the film doesn't have, though, is an ending.
Now don't get me wrong, it's not that Piranha has a bad ending. Nor do I mean that it just abruptly cuts to black and no credits roll, leaving the audience confused as to what's going on.
What I mean is that, if you broke down the script in normal screenwriting terms, the film gets to the point that would be the end of the second act/beginning of the third act (when the hero has gained new knowledge both about themselves and the threat they face) -- and then the credits roll. It would be as if Aliens ended with Ripley flaming the eggs right in front of the queen, scooping up Newt and making a break for it.
If I had any respect for Aja at all, I'd say it was a brilliant subversion of genre convention. But I don't. (I thought Haute Tension kinda sucked, the less said about his Hills Have Eyes remake the better, and Mirrors was just ugh.) Instead it feels like he ran out of money and/or just got bored after doing the big attack & effects sequence he wanted to do, and so he didn't bother even finishing the story.
At best, it's the clumsiest attempt to leave a horror movie open for a sequel in history. At worst, it's one of the most incompetent film making decisions I've ever seen.