American criminal justice succeeds in one respect -- it solves crimes and brings wrongdoers to justice with pretty good reliability. This is more than can be said for courts in most nations, and shouldn't be underestimated.
However, when scholars compare the United States with other developed countries, they usually come away impressed by the efficiency, reliability, and consistency of civil-law justice systems. Here's David T. Johnson on American prosecutors, after he completed an in-depth study of Japanese criminal justice (I've removed the citations):
American prosecutors are anchored in a contradiction. On the one hand, they are expected to be neutral, independent "ministers of justice," not simply advocates seeking conviction. As such, they are obligated to exonerate the innocent with the same vigor and determination with which they pursue the guilty. On the other hand, the ability of American prosecutors to fulfill this obligation is undermined by the chief prosecutor's continuous, direct dependence on the electoral scrutiny of a public which fears crime and demands that officials get ever tougher with it. . . .
Of course, accountability to the public constitutes the chief justification for the American prosecution system and is, in the eyes of some, an almost unqualified good. Nonetheless, electoral accountability has many unfortunate, unintended consequences. Public opinion research reveals that American voters know little about crime or criminal justice and are frequently hostile towards judges and prosecutors. In particular, many Americans believe prosecutors make so many concessions to offenders that the "bad guys" are neither charged nor punished as harshly as they deserve. Scholars have shown that American prosecutors actually concede little, but public misperceptions continue to push prosecutors (and the rest of the criminal justice system) in an increasingly punitive direction. Many lament the results: large and growing racial disparities in arrests and incarceration, badly overcrowded prisons, scarce resources directed away from more effective crime control policies, little discernible effect on the crime rate, and countless miscarriages of justice.
[David T. Johnson, The Japanese Way of Justice: Prosecuting Crime in Japan, p. 30].
You hear critiques like this frequently from foreign observers of the U.S. criminal justice system, but Johnson is an American. Like most Americans who study criminal justice in other advanced nations, he comes away deeply critical of American practices. Another example of this -- from a former prosecutor, no less -- can be found in Trials Without Truth, in which William Pizzi comes away impressed with Continental criminal-justice systems for many of the same reasons Johnson is impressed with Japanese justice (which is heavily influenced by German jurisprudence, since Japan adopted much of its criminal law from German sources).
American scholars return stateside and criticize electing judges, electing prosecutors, and the hopeless overload and underfunding of the justice system, which leads to massive amounts of plea-bargaining. What they see in foreign criminal-justice systems is (1) a much more subdued role for attorneys; (2) a focus on gathering all the relevant facts without hindrance from complex procedural rules; and (3) developing a comprehensive picture of the offender's background, and individually tailoring sanctions to his circumstances. More conservative commentators like Pizzi appreciate the matter-of-fact, truth-oriented investigative style of civil-law legal systems. More liberal commentators cannot fail to note that the punishment handed down in these systems is much more lenient and individually-tailored than it would be in most American courts, especially state courts.
It reminds me of my first criminal law prof, the late, lamented Daniel Rotenberg, who once told us: "American law is pretty influential all over the world, except for our criminal-justice system. Nobody wants that!"