In a quick update to yesterday's story, it would appear that the Sonic Generations demo will only be available to PSN and Xbox Live users for twenty days. It went live this morning (REMINDER: It's live on XBL. PSN updates itself later in the day) and it's set to expire July 12, so snap it up when you can.
Furthermore, the demo will not include the "modern" Sonic stage. It will just be Classic Green Hill. This really interests me, as it implies SEGA knows that the "modern" levels are nowhere near as good as the classic ones, which is the sense I got from my preview at E3. Maybe SEGA doesn't mean to communicate that, but it's the message I'm getting.
In any case, I really did dig the 2D stuff, so download it and see if you fancy it too.