By no means the best DOS game by any objective measure, but my favorite is Sierra's Hoyle Card Games, specifically Volume 1 from 1989. I don't even wanna think about how many hours I spent playing cribbage against the bulldog npc as a kid! Playing card games with King Graham and Roger Wilco was a special kind of silly, I love it.
...To this day, I'm still not 100% sure how cribbage even works.