This is actually a ps3 video, but this is pretty much what you do when you unlock Green Goblin. Just run around, doing absolutely nothing.
[youtube=425,350]iilhrdPxIm8[/youtube]
You can download New Goblin from the Xbox Live Market place for 250 points (that's about 3 dollars).
It's fun for the first few seconds, but it gets real old because you can't play through story mode.
I really hope they just release Venom. Also when you save civilians, people still call you Spiderman.