Unorthodox shapes are achieved by using entities (for walls or anything else) which you can rotate or place anywahere you like and they are not restricted to the grid size. The end result is the same as using any world object (wall, room, etc) which are restricted by the world grid/tile size. Ramps are available as default segment types or you can make your own.
You cannot change the grid size, but can put pillars or other objects anywhere you like by using the entity method as described above.
Lighting can be affected via the game settings and lights themselves have a range of settings that can influence the overall lighting ambience. You can have areas that are as dark as you want given human vision capabilities - almost black by using a combination of the available lighting capabilities mentioned.