Info from BetaWiki and TCRF
Build 8102, aka Developer Preview, has exclusive games that are not in the final release or the Microsoft Store. Due to API changes between the preview and the final release, they cannot be used on the final release (source). There is an upload of the fixed games (along with some other exclusive Metro apps) on archive.org.
According to the screenshot on BetaWiki, build 8250 aka Consumer Preview has Pinball FX2 and "Solitaire". The icons for both have an "Xbox Live" banner that is different from the green one seen in Windows Store games. The icon for "Solitaire" is identical to "Microsoft Solitaire Collection" (minus the Xbox Live banner).
Release Preview is build 8400, which is not far from the last known build to have Aero transparency effects, 8427.