I say this because I love you. Don't buy this game!!!
The save system is GOD AWFUL. On one of the first few levels you have to fight some kind of Intergalactic gladiators (Don't ask!). You beat him once and 1 becomes 2, 2 becomes 4 and on and on and on. Each guy is defeated pretty much the same way. The same combo of moves over and over and over again. Then after what seems like FOREVER you find yourself pitted against the level boss. Don't die because when you do, you have to start the ENTIRE LEVEL over again. No check points. No Saves allowed. Superman has powers. Like heat vision, and cold breathe. The problem is most of your enemies can block these powers. So they are pretty much useless. Talk about a tease.
The game IS open ended. But good luck finding something fun or of interest do in Metropolis. Boooooring...
Do yourself a favor and punch yourself in the baby maker. It is much more enjoyable and not as painful as playing this game.