A parser system would allow the player to type in questions/answers or topics of interest during the conversations, instead of choosing from a list, and using "dialogue trees". This was used in many early pc games and although I never played Arena, I know this kind of thing was used in some situations (answering some riddles for example). With advancements in technology since the these games however, a parser system will only be better.
http://alice.pandorabots.com/
This system would make you have to listen, and converse with the NPCs on a different level. Instead of just clicking the highlighted conversation option, you have to listen to the conversation for points of interest or questions in order to get the info you need. When you are asked a question you have to answer it, making things like riddles possible (instead of save/load, process of elimination affairs)
If you type in something unrecognizable, then the NPC could just say "what?" or "can you say that again" or if you type something incoherent (like "aajdvcfaxcn") they could say " you speak in a strange tongue...".