You did read the Death of Superman, right? He did try outthinking Doomsday, but it didn't work as while Superman tried to come up with something, Doomsday would kill, say, half of a town or so.
and Superman did go at the full range of his abilities, though he didn't really cut loose on Doomsday until the very end of the fight. Before then, he'd used flight (getting him away fromt he small town in Ohio where Mitch lived), full force heat vision (in conjunction with the rest of Justice League America), super speed, and other abilities against Doomsday. The problem was that Doomsday kept getting more and more powerful, and Superman could never take the time necessary to deal with him earlier in the battle because Superman was busy, you know, saving people.
That's the thing that gets me with the Death of Superman, when people talk about it. Everyone just says Superman went toe to toe with Doomsday, when that's not all that happened. Throughout the entire fight, Superman is saving people, and it's not until he's already beaten bloody, with poison coursing through his veins, that he focuses all of his power against battling Doomsday. Superman was staying true to his character and fighting to save people right up until the end, when he was forced to come to the conclusion that the only way to stop Doomsday was to kill him.