You win some, you lose some. Support for Windows 7 and Windows Server 2008R2 was added, but you're unlucky if you're still running Windows 95, 98, or Me. Then again, if you're still running any of those three, you deserve to be unlucky. Or you got bored with self-deprecation, and moved beyond it.
Of course, this release brings more than changes in platform support. For instance, the mount table is no longer stored in the registry, but has been moved to
/etc/fstab.d/$USER instead. The support for pathnames has been extended beyond the old 260 characters border. Cygwin now supports up to 4096 characters, but it will try to support even more characters, up to the Windows maximum of 32767 Unicode characters.
You can now have multiple installations of Cygwin, but you'll have to keep them isolated. IPv6 support has also been added to the mix, and internationalisation support has been improved, and the default character set has been set to UTF-8.
The list of improvements goes on for a while, so be sure to check if your pet bug has been fixed. You can download the new release from their website, but note that if you're upgrading from a 1.5.x release, you'll have to do some manual labour to accommodate for the mount table changes: every user has to run
/bin/copy-user-registry-fstab once after the update.