|I've always liked Johnston and tend to look on him favorably. But Robert is certainly right about his role in the loss of Kentucky. It's really hard to overstate how disastrous that was for the Confederacy, and I don't believe it was inevitable. Johnston wasn't the only one to make mistakes there of course, as there was plenty of blame to go around. But he probably comes in for the lion's share of criticism, or close to it. I think he did better at Shiloh though, despite the mistakes that were also made there.
As for his historical reputation, that's probably intertwined to some extent with the Lost Cause line of thought that emerged after the war. But it sure wasn't the case prior to Shiloh. It's interesting the way his reputation went from potential savior in 1861 to criminally incompetent after the Kentucky disaster, and finally to southern hero. Johnston's death at Shiloh, helping to lead a charge no less, went far toward redeeming him in the eyes of southerners at the time, and the eyes of history later on. In fact, his death in battle just about erased whatever "sins" he may have committed before then. You don't criticize a fallen hero.
Beauregard certainly wasn't shy about criticizing him though. But Beauregard himself came in for criticism as the general who threw away the victory Johnston was about to win. I don't buy that, but it's one of the most persistent storylines of the battle.
As to criticizing Johnston for 'leading from the front,' and acting more like a small unit commander than an army commander, I see the point, but I've never been sure about it one way or the other. I think it depends a lot on whether his actions did, in fact, cause him to lose a grasp on the overall battle. If so, then he was guilty of repeating his Bowling Green mistake, where he became fixated almost exclusivity on what was directly in front of him. But I'm not totally convinced this happened at Shiloh.
Plus, while he was close to the front for much of the day, he generally stayed back somewhat. In fact, for most of the morning he was located in and around the captured camp of the 18th Wisconsin, until he received word of a possible enemy division beyond his right flank. (An exaggerated report, as it turned out of course, but he did not know that.) His actions in leading the charge in which he was shot strike me as a spur-of-the-moment decision, made for the purpose of helping to inspire his men in a charge on the all-important right flank. We can call him reckless or maybe even foolish for doing this and perhaps he was. But other commanders did such things at times. Grant himself came within inches of death at Shiloh, when he too was near the front lines. The bullet or shell fragment that struck his scabbard hit with enough force to break the sword inside. Anything that hits with enough force to break a sword carries enough force to kill a human. So Grant was indeed "lucky" compared to Johnston.
I think Johnston will indeed remain that "what if," or as I call him, a question forever in search of an answer. We just don't know what sort of commander he might have made after Shiloh, win or lose. He showed far more resolve at Shiloh than he had shown in Kentucky, and I think that Charles P. Roland is probably right, that he had the capacity to learn from his mistakes and grow as a commander. (I think this was Roland, although it might have been Johnston's own son.) That's what Grant did. And perhaps the lesson of Robert E. Lee in western Virginia could be instructive here. Lee did not exactly get off to a stellar start in his Civil War career, but he seemed to improve somewhat later on. Maybe Johnston would have done so as well. There's just no way to know.
On the whole, going only by what he actually did in the war, I think the scales balance out on the negative side for Johnston. But they had not settled into a final position by the time he died, and may have started to tilt back in the other direction. So for me at least, he still remains that perpetual question mark.
For whatever it's worth, I think Grant would still have proven to be the better commander. No one was ever able to beat Grant in a campaign. Johnston may have proven to be the exception given time, but it would have been a very tall order. As Johnston and Beauregard learned at Shiloh, Grant was a tough out.