VLC, in my experience, plays 90%+ of DVDs perfectly (actually better, since now everything is skippable and you get significantly more rendering options than any other player).

The few DVDs which malfunction are typically published by Disney in the last few years and contain DRM specifically designed to break unlicensed players. VLC have been very active in fixing these issues, and have in many cases.

But if people plan on using VLC just be aware that the rare DVD won't work well or at all. Still the best DVD playing software I've used, including paid software.