Today a Korean website has leaked the opening sequence of Sonic Unleashed, due to be released this month. The intro is very cinematic, and features a Back To The Future-style orchestral score.
Also leaked was the introduction of Apatos and the exploration of the town. It seems that Chip has replaced Tails as Sonic's sidekick (sniff). Aside from that, the stage looks very good. Apparently, Act 2 of Apatos is played, so a Werehog stage is Act 1; however I couldn't see this on the low-quality version.
Both videos are of the Xbox 360 versions. Some websites also claim that in the final build Sega is hoping to achieve 60 frames-per-second, a vast improvement of the 15 frames-per-second seen at E3.
EDIT: Sega Europe has pulled both videos and numerous mirrors due to copyright infringement. You'll just have to find another mirror or wait until the game is released!