http://www.valvetime.net/threads/source-2-left-4-dead-2-prototype-screenshots-leaked.244266/
The first slide, shown above, features an updated version of the the Plantation level from Left 4 Dead 2 and highlights the significant increase in detail possible on the Source 2 engine, with noticeably enhanced foliage, large amounts of high quality destruction, and improved lighting and shadow effects. While this slide alone is very interesting, the presentation actually features a total of 20 slides. Unfortunately, 13 of these slides remain obscured from view, so we're not entirely sure what they may be discussing.