Just like the first game, I've completed Super Mario Galaxy 2 with its own 120 stars, but not without some sweat and tears. While I believe the difficulty factor was increased a notch, it didn't feel as difficult as the first one. However, they did bring back that cursed 8-bit Mario level that everyone practically hated for its purple-coin challenge with an added twist, and made a rolling-ball level on a Rainbow-Road track. Kudos to Nintendo for busting out the familiar "OMGWTF was that" references!
And like the first game, there's another set of 120 stars to collect in the form of Green Prankster stars littered in all the levels. Basically, for every star that existed in each level, another green star is there. And some of them are located in very sneaky places! I'm into 160+ stars now, so look out in the future for another post for possibly a FULL completion of a game!