It was in my gold box yesterday (or whatever it's called now) for a few dollars more off, and then I added the ECA discount, so I got it for like $42, 43.
The demo was pretty great. I'm a little worried it'll get too tough at some point, but what I played of it was fun. I'm a big fan of Crackdown, and I think anyone who likes that will like this (though they're not identical of course, the powers are real different, etc.)
EDIT: Isn't Prototype kind of in the "open world superhero genre" too? I love these games! I know when I was playing the Infamous demo, I thought at one point "I just can't believe this game exists and I'm getting to do this cool stuff". I remember the horrible days before The Matrix and the first X-Men movie when basically there weren't any good superhero movies (although the Shadow was awesome, so maybe that was the first?) And superhero games were almost as bad.
One thing I always hated about superhero games was how you were never powerful enough, and never could use your powers more or less indefinitely. That is one thing I'm a bit worried about in Infamous, since some powers do have to be recharged, though even your basic "force lightening" is pretty danged cool and clearly better than a gun (aside from the "chain link fences are this guy's kryptonite" thing
D )