It's true: the Xbox One will not play your Xbox 360 game discs, nor will your Xbox Live Arcade games transfer (not to mention any other content that's dependent on the 360's hardware architecture, anyhow). That Gamerscore you've been earning, though? That's gonna transfer. As will your Xbox Live Gamertag.
Sadly, due to the x86 architecture of the Xbox One, the PowerPC-based 360 titles simply won't run on the hardware. Microsoft's not super worried about consumer reaction, though, telling Engadget, "We care very much about the investment people have made in Xbox 360 and will continue to support it with a pipeline of new games and new apps well into the future," a Microsoft rep told us. That said, Xbox One is designed, "to play an entirely new generation of games -- games that are architected to take full advantage of state-of-the-art processors and the infinite power of the cloud."
We got a glimpse at some of those new games this afternoon, but we expect to see much more at E3 in a few weeks.