I love this! This is the start of the city builder I've been waiting for! Here are a few things I would love to see added/changed:
Intersections like Jiri_one mentioned, as well as bridges and overpasses.
Water and rivers like Ms .45 said.
I think it would awesome if you could adjust the hight of land so you could make hills and cliffs.
It would be cool if when there were two roads going the same direction side-by-side you could choose to merge them to create a "highway"
I would like it if the grid "snapped" a bit more. I find that when I want to place a building or road in between multiple other constructions i have to be very specific as to where my cursor is. This would make it easier to use your game.
Another thing that would be nice is if the button for buildings was closer to the other two current buttons for objects. That way you wouldn't have to move your hand so much.
I am just starting to learn to code so I don't know how much of this stuff is possible but I hope it's helpful. I can't wait for the next updates!
P.S. I LOVE your artwork on twitter and especially your pixel art style. This is the first game of yours I've played and I'm looking forward to playing your other games as well!