Regarding WA and WWP Remastered:
Clean & crisp visual style, with well-defined maps, sprites, and HUD elements on dark backgrounds.
Runs on weak computers, but has gameplay as deep as any modern AAA title.
6 player online with easy-to-use chat interface, plus direct IP, LAN, and hotseat functionality.
Has the definitive physics engine of the series. Highly accurate, the outcome of nearly any move can be predicted. Later engines have more random elements.
Has the definitive Ninja Rope of the series. Insanely flexible, it has given rise to its own robust community.
Custom flag and gravestone support, as well as offline custom soundbank support.
Deep atmosphere, with an excellent ambient soundtrack.
Regarding WA only:
Use any image as a map.
All matches saved as replay files - schemes, maps, and video and be exported from these.
Features HostingBuddy, a workaround for firewall issues.
Support for mods such as Rubberworm and Project X.
Nonstop support and online activity since 1999. Features added over time include giant maps, ultra-high resolution support, and numerous interface, compatibility, and gameplay improvements.