It's funny how the game has changed with respect to spells. It used to be that almost every spell level had an instant win spell: sleep, web, and stinking cloud come to mind from my 1e days. Basically, you'd swap your instant win spell of level X for the instant win spell at level X+1 as you progressed.
Playing a magic user back in the day was much different than playing today's wizard. You'd stand at the back of the party, chucking darts and waiting for the one battle that you absolutely needed to win. Out would come your sleep spell, then the group would head back to the surface. It's crazy to compare playing my 1e MU to playing my 3e arcane casters.