completed the game on Easy difficulty.
 completed the game on Normal difficulty.
 Looking at my old PS memory card. I distinctly remember the final escape from Carnage-Ock, but my savegame has no record of me completing the game.
 ... Or does it? The first savegame on my memory card is early in the game, but on hard difficulty. And when entering the costume viewer, I can see that I unlocked these costumes: Spider-Man 2099, Symbiote Spider-Man, Spidey Unlimited, Scarlet Spidey, Ben Reilly, and Peter Parker. You get Symbiote Spider-man for finishing the game on any difficulty, and I don't have Captain Universe, which you get for finishing on Hard. I do have Spidey Unlimited for beating the game a second time, so I'll assume that I finished it at least once on Normal.