It's too bad all the screenshots are of open-source windows ports of stuff, and stuff that's otherwise going to be really well-behaved (ie, not use secret API's)

Check out the second link, and scroll down. A lot of proprietary Win32 application work just fine.

From 3D games like Unreal Tournament to Adobe Photoshop, Screensavers, XEmacs... like in Wine plus apps like CD burning apps and similar that require NT drivers.

As driver support is still an issue on desktop Linux (3D graphics, HD audio, proprietary hardware cards, etc), ReactOS has a great advantage over *nix operating systems.

Notepad++ isn't a windows port, and is in fact so dependent on Windows APIs that there is no Linux version of it.