Concept was good, but the controls suffered
It was a really fun concept, so that's where a lot of the points came from on this game. I even enjoyed most of the upgrades even though I really didn't notice much of a difference in the piranha attacks. It would have also been nice if the piranha was large enough that I could have seen a visual change in its appearance other than on the upgrade screen. Like the teeth got sharper on the upgrade screen, but it was the same fish on the game screen, it just seemed to take away from upgrading.
My biggest complaint were the controls on this game, they were pretty unfriendly to the user. I found it very difficult to keep good control of my fish unless I moved my mouse extremely slow, and even then it wasn't too accurate. I also found attacking people painfully frustrating because even moving the mouse around like crazy wouldn't necessarily ensure that the piranha would attack. I would of been more happy if this was a "awsd" game, or God forbid, a game where I had to click to attack. At least with clicking I would know that I was attacking, as is I just kept moving my mouse around like crazy hoping to hell that it would attack.
A few other things took away from the game also. When I knocked someone out of a boat, the person still in the boat would continue to move on ignoring the fact that the only other person in the boat with them was gone. Have them at least stop the boat and try and help the person back in. This goes the same for the people in the kayak, have them at least try and get back in their boat, if they do then have them paddle off faster, it would make it more interesting Also, the propellers would hurt me, but the person in the water that just got run over by the propeller didn't get hit at all, seemed like a glitch at first, but then I realized that was the way it was made.
Again, a really good concept, and with a few tweaks this could be a really good game. Hope to see another one.