Piranha 3D was a lot of fun. I feel like the film makers knew what they had. I mean there is no way a film such as this is going to be a classic, remembered as a cinematic marvel in years to come. It was what it was and that was a lot of trashy fun. Throw some blood and boobs on screen and have a bit of fun with it and that's cool. It does it perfectly.
The difference between 3D and 3DD is 3D knew where to draw the line. 3DD is like an unfunny friend who can't tell a joke. They mess up the delivery and so they keep trying to over explain it digging themselves into a deeper and deeper hole. Eventually you are just left with a mess.