The one thing that everyone who was there seemed to agree on was that it was a very strange affair. Whatever Custer's real tactical intentions were, a massacre wasn't one of them. Custer did have his vainglorious tendencies but completely discarding his intelligence information as he did was not typical behavior. And numerous spoken histories on the part of the Sioux contained a sincere disbelief that he could have committed the series of blunders that placed him three-quarters of the way up a poorly defensible ridge.
Much of the mythology that surrounds the event is a function of Custer's wife, who tactfully omitted certain particulars (his Native American mistress, for one), and of Buffalo Bill's show, that sensationalized the battle and turned it into a media event. Both Sitting Bull and Crazy Horse strike me as rather admirable men, and so, for all his faults, does Custer, whose career paralleled Crazy Horse's in some very interesting ways. But of them, Sitting Bull was by far the superior strategist. IMHO.
It is strange. During the Civil War, Custer would scout his enemy carefully and then attack fiercely and intelligently. If he took chances back then, it was understandable since a loss could mean losing the war. He could easily afford to pull back against the Indians and hit them a few days later with much better forces and with better geography.
His screw-ups at the Last Stand don’t really fit Custer’s style. By then he had gotten quite a head for fame, so maybe he had been talking up the upcoming battle with his attached correspondent and didn’t want to be seen retreating from a fight.