On a planetary scale. Just spitballing, no maths. (assuming some sort of life as we know it could exist)
The difference in the speed of light and sound would increase. So Eg you would see the lightning alot earlier than hear the thunder. That lightning would also be brighter and possibly longer lasting...so no watching lightning storms without protective eyewear!
Also, in talking. The person you listening too, would appear to finish talking before you heard what they said. It would be like watching a badly dubbed Chinese movie!!! Or like talking on a bad international phone call.
You won't be able to see further, as the curvature of the planet would remain the same but you would be able to see clearer for the same distance. So no hiding in the distance hoping no-one sees you on the battlefields. Think elf-like vision.
The sound barrier was broken and now we can travel at mach speeds. If you double the speed of light, you have just increased the chances of NEVER creating faster than light travel. There goes FTL, and galactic and intergalactic space travel... and time travel for the time being.
No visitation by alien's, unless they are on multi-generational sublight ships. Which makes friendly encounters less likely as they will be desperate for refueling/restocking. So yeah, think Independence Day/Battle Los Angeles rather than E.T.
Although you would be able to see them coming a lot sooner so you would have time to prepare and grab your towel! It would be possible that you could set up a communication network with other planets. You would never meet them, but you could chat and share ideas via a light beam (as long as you take care not to burn out the receivers with too focused a beam. Whoops! There goes your friendy communication attempt and now they are coming to get you).
Light could possibly travel further into the oceans (assuming the light didn't just burn off all the water) this would increase the 100-200 meter zone where most (not all) life exists in the sea. If the light is too harsh on land, it could result in those fishy ancestors of ours never having left the ocean and an underwater civilisation may have evolved instead.