As Harsh points out, there is a major difference between those writing specifically about McClellan (or was until Stephen Sears wrote his tomes) and those writing general histories of the war. The former, whilst admitting his faults generally found him capable whilst the latter had to fit him into their vision of the war. Since he was the foil to the now eulogised Lincoln, he had to be the fall guy for Lincoln's mistakes. It is the latter group that have dominated the debate since Bruce Catton put forward the idea.
I tend to agree with those that were actually there and witnessed the events. McClellan was a good but cautious general (IMHO like a more impolitic Wellington), and probably the best general the Army of the Potomac ever had. Those far removed from the events tell a different story however....
He would have been a great general in any society other than a democracy with civilian control of the military. A man who refuses to see his commander-in-chief or reveal anything of his ideas such that the Commander-in-chief would not sack him is not exactly one who understands democratic war in the way that say, Eisenhower did. Or Montgomery for that matter.
McClellan was a bumbler who saw the Confederates as overwhelming him in numbers when that was not the case. He spent an entire month with 90,000 troops besieging 17,000 to which Joe Johnston said "Only McClellan would have failed to attack." Like Braxton Bragg he also had a weakness that when he planned something, he *planned* something and his plans never took into account the reality of Murphy's Law.
... and so we see the bias.
Since Lincoln is "America's greatest President" [sic] then he must have done no wrong. Ergo the problems must have been due to those who opposed him, like McClellan. McClellan is reduced to a foil for Lincoln, which was a useful narrative technique when introduced.
Of course, Lincoln was,
at the time, considered the worst President in US history (see Tagg's "
The Unpopular Mr. Lincoln"). The period of him assuming direct command of the armies can only be considered disasterous (see, for example, Stoker's "
The Grand Design" for discussions of high level strategy and war aims)
Jefferson Davis of the Confederacy was equally unpopular. The difference was Lincoln accepted McClellan's snubs if he'd ever actually used the Army of the Potomac, instead of treating it as a 168,000-strong bodyguard. Davis never forgave Johnston or Beauregard any of their snubs and disagreements, which led to the Confederate fuck-ups in the Western theater that a good general like Grant was more than willing to exploit, same as Lee's victories were less his virtues than due to exploiting his enemies' failings.
Which it must be said is part of war as it is, not as people want him to be.
It must also be noted that Lincoln assumed direct command with Stanton around the time of the Valley Campaign and their strategy *was* what was necessary to bag Jackson. They just entrusted it to political generals who weren't capable of counting to 21 without dropping their drawers.
This is a rather leading statement/ question.
You make the implication that obviously McClellan was incompetent at Antietam, and everyone knows it. Ergo is anyone crazy enough to suggest otherwise?
The answer is of course, lots of people have written of his competent conduct of the battle, but most are long dead since they were generally witnesses to the battle themselves.
Recently (well 12 years ago now!) we've of course had the definitive study of the Maryland Campaign in Harsh's "
Taken at the Flood", which concluded much what all the witnesses concluded; McClellan made the right decisions given what was known.
As Mannie Gentile has
pointed out, the current notion of Antietam as "badly fought" comes from a series of biased, rather vitriolic books which do not give a balanced view.
Did he now? He was against, along with his Commander-in-chief, the idea of the "harsh remorseless revolutionary war" but with Lee backed into a position that if he had ever followed the practice of Grant, Sherman, Jackson, Longstreet, and both Johnstons of leading from the front he might have actually noticed that he could have used his army to pin Lee's along the Potomac while sending Burnside's corps around behind the position.
Lee's career would have ended that day, and the Union would have had a war with more victories than defeats. Instead McClellan made very poor use of his troops and as always was well behind the line to the point that his subordinates directed multiple actions instead of a singular one.
His gravest defects were never using his numbers effectively (hell, Joe Hooker had a better idea of how to use the Army of the Potomac than he did. He was equally good at executing it, however

) and being well away from the actual combat lest he see war as it was.