It was an excellent idea, but executed in such a horrible way it's sinking us all except Germany, Netherlands, Luxembourg and the members that didn't enter the Euro. As RedInker pointed out, the bureaucracy is insane, the committees of burosaurs have far too much power despite not being elected by people like the Europarliament.
The Euro itself was a good idea, but it became a trap, it created real world inflation (despite the official one being low) and it has stiff and unreasonable rules that make things worse for states in difficulty. The Euro, to sum it up, has all over itself the signature of my bastard, incompetent, corrupt, thief fellow citizen Romano Prodi.