I still think the original Saints Row 3 is the most graphically beautiful open world game ever created by Volition. I know Saints Row 2 has a beautiful looking city, but the rendering technology just doesn't hold up today. The lighting in SR3 -- especially at night -- is really beautiful. Yes, it's mostly light mapped, but its utilization of planar reflections instead of screen space reflections on the wet street at night makes the city come alive! And the lit rain effects, a technology pioneered by Volition, really adds significantly to the realism of a rainy night. Okay -- so the new engine will add a bunch of new technology -- but it really depends on how well it's implemented. I've seen beautiful light mapped games, and also some not-so-beautiful games that use much more advanced technologies. Throwing technology at something doesn't necessarily make it better, and can sometimes kill performance (evidenced by Agents of Mayhem).
I still wish they'd fix the broken traffic splines (or buggy construction spawning) which causes traffic to turn around for no apparent reason. And that really annoying infinitely shifting transmission in all the cars. When I drive down the road, the car just keeps shifting and shifting and shifting forever. It's incredibly annoying. I don't think anyone ever figured out how to make mods to fix those issues.
SR2 might not be pretty, but SR3's character model textures are some of the worst I've ever seen. I find it puzzling how they somehow went backwards and didn't allow for a dynamic day and night cycle, it doesn't make sense. The environment is rendered fine, but it's a shame the city lacks anything of interest.