(This is for all three of them)
Rhygar is a little rough around the edges, lacking an ending, and it uses a lot of exclamation marks and ellipses, not to mention every door is "locked tight." But while some aspects haven't aged well, the majority of it comes out shining. It's the best attempt I've seen at a really long epic game implemented in ZZT -- whereas most attempts fluster out after the first hurdle or two, Rhygar goes much further. It's not too hard and the RPG fights are admittedly lackluster near the beginning, but this helps make the adventure itself the focus of the player's attention. The writing and storyline are involved and interesting. It's a shame it was never finished. Despite this, it's way, way longer than a lot of similar efforts; anything less than a full score would neglect this fact. Rhygar is a gem.