River City Ransom and the Capcom D&D games are pretty much my favorite beat-em-ups of all time. Both Tower of Doom and Shadow over Mystara actually manage to capture the feeling of the tabletop game really well. Good visuals too, with detailed characters and some cool enemy designs. The optional Red Dragon in Shadow over Mystara still feels pretty damn intimidating. I was so happy when Iron Galaxy's compilation came out last year.
Retro Gamer had a pretty comprehensive article on the D&D games a few years back, which I wholeheartedly recommend. Capcom hadn't really worked with Western developers (in this TSR) before, so there was a bit of a culture clash. Alex Jimenez constantly had to negotiate with the two companies during development. For example: Capcom wanted to put a steamship in the game. TSR wouldn't allow it since that kind of technology doesn't exist in the Mystara setting. Jimenez explained this to the team in Japan, who tried to talk him into convincing TSR. However, this proved impossible, much to Capcom's disappointment. I think the article mentions a few more stories like it, so I should dig that up.