Weclock: I just get ticked off at people calling it "revolutionary" and saying stuff like "nothing was ever like this before!"
TheCheese33: Of course it's been done before, but not on consoles. Also, the two are good at different things. For example, if I wanted to create some awesome flying apparatus, spawn hundreds of zombies to attack me and my friends at our homemade shelter or create a machinima recreating a scene from Saturday Night Fever, I would use Garry's Mod. However, if I wanted to create an entire platforming level, I would go with LittleBigPlanet.
you could easily make a platforming game with garrys mod, also there are quite a few that are really good on consoles, that maybe don't have the same level of customization, but I would think of lode runner as being one of the earlier games to have an appropriate level editor. and I also like the one in loco roco.