From the beginning, ACTA has been negotiated in secret with the public and consumer interest groups excluded while entertainment industry lobbyists have actively participating. The secrecy has even extended to prohibiting elected officials from finding out what their own governments were agreeing to.
Despite assurances by the negotiating parties that ACTA would not require changes to the laws of any participating country, every draft of the agreement which has been leaked have shown that to be absolutely false.
In the US, officials from the US Trade Representative's office have defended ACTA by saying it's an executive agreement, rather than a treaty, meaning it wouldn't require changes to the law. ACTA critics have pointed out that this is merely an excuse to avoid having the agreement debated in the Senate.
More importantly, there are significant questions about the president's authority to enter into an international agreement over a matter which the US Constitution specifically gives authority over to Congress.
It also appears many of ACTA's provisions violate fundamental rights recognized in the EU.
Hmmm... well, that's no good. But will it actually be enforced? Last I heard companies could have gameplay videos taken down just because it's their game. Someone feel free to correct me if I'm wrong though and/or expand on what I said.