https://redream.io/
Redream is a new Dreamcast emulator that is knocking the socks off of the competition. It has great compatibility and the ability to scale the games up to 4k and beyond. Dont believe me:
https://youtu.be/IZ0Vq9oxK7s?t=291
How about some 4k Powerstone
Or 1080p Gauntlet Legends:
https://www.youtube.com/watch?v=IUR-vczVifo
There are many videos of Shenmue, MVC2, and Daytona USA.
But just look at how photorealistic these trees look: