Okay, now, I've seen Piranha, I've seen Expendables, I've even seen Centurion (I do consider myself a movie nut as on average I'll see two flicks a week, and that's just in theaters). I'm still calling BS here.
Now, Piranha is probably still the better movie for one reason: editing. Nevermind the 3D aspect, Expendables had some serious artificial shaky cam problems in a few scenes, which was baffling since a couple of scenes had great shots, like Terry Crews using his big-old shotgun repeatedly. Piranha 3D meanwhile has none of that, and while the violence in Expendables was cartoonish for the most part, Piranha's own violence actually felt more realistic even though it had acts that were physically impossible to do while dying. I say this because seeing a guy get flat out murdered by Statham and Li was awesome if a bit gross while seeing a porn star get slashed in half made me quite queasy. 3D may have been a factor there though.
Still, for everything else, BS. The plot was fine. It wasn't epic, no, but it wasn't crap by any means. It doesn't need anything to excuse its short-comings as it still, at the end of the day, was a solid flick, though certainly not something I'd expect people to tout as being best film of the year, at least in general. Piranha and Expendables also made pretty good use of their cast, each actor and actress in both playing to their strengths. Each film does also have a weak link however, Piranha having Ving Rhames really phone it in until his final scene while Expendables had Randy Couture who's a pretty awful actor but at least he had a good fight in the end. Really the only things needed to make Expendables the stronger movie than Piranha would have been to not shake the camera so much and instead of giving everyone new names give the film a sense of meta by having them all use their real names. Given that people will just refer to the cast mostly by their real names anyhow it kind of makes sense that they'd do that in-film.
I do want to call out the claim that Piranha's a better movie for having woman on woman action in 3D. While you can't necessarily find that on the internet (Yet, and even then I didn't look), its a movie about killer fish. The scenes add little to characterization and are really just there to pander to the male audience, giving the film padding and exploiting its R-rating. While I'm fine with exploiting an R-rating, praising the movie for using a woman's nice rack over a film that actually tried to be a little deep (thank you Mickey Rourke) while still having a great deal of fun is total BS. At least in Expendables there were no pointless scenes (cue someone pointing out a scene I'd forgotten about).