Brettd is, as usual, right on with his answer. However, I would add one thing to his answer that will supplement it, not dispute it.
As he says, the main difference was that Ushijima defended in depth. But the point that needs to be made here is that he was trying hard to defend for as long as possible and to inflict the maximum possible casualties on the enemy. This may sound obvious, but this is not really how things were always done. In many cases, other Japanese commanders opted for what the Japanese called "honorable death" instead of fighting for as long as possible.
The Japanese word for this "gyokusai" and it is written like this:
玉砕. That first character means "jewel" and the second means to break or crush. That shows the Japanese attitude towards death at that time. They felt that their own deaths and how they happened were more important than killing the enemy.
Because of this, Japanese commanders on places like Saipan tended to order "gyokusai," or what Americans called "banzai charges." These allowed the soldiers to die in an honorable way, but they were much less effective than holing up in caves and fighting to the death would have been.
On Okinawa, Ushijima forbade such things and for the most part made that stick. Thus, his defense was much more deadly than that mounted by other commanders on other islands.
So, I'm agreeing in general with BrettD. But I would shift the focus to the idea that Ushijima's goal was to kill more of the enemy and delay their victory, not to ensure that his own soldiers got an "honorable death."
Unlike in many islands such as Pelelieu and Iwo Jima, the Japanese commander of the Okinawa defense, Lt. Gen. Mitsuru Ushijima, decided against fighting the American landings on the beaches, in favor of defense in depth.
While other landings had been costly for the Americans, they had all been successful in the end, so Ushijima accepted the fact that the Americans were coming ashore, and instead chose to defend the most rugged areas of the island, and to create fortified defensive lines. Also, by not firing on the landings, he did not reveal where his army or their main guns were located until the US Marines and Army stumbled into the line of fire.
So you could say that Ushijima was more pragmatic in his approach to defending the island, in no small part, perhaps, to the fact that Okinawa was considered a part of Japan and not just some outlying territory. The ease with which the Americans came ashore quickly gave way to grinding and ugly combat which lasted for nearly three months and cost the Americans more than 12,000 dead and 50,000 wounded.