What should a good solder joint look like?

A good solder joint should have a smooth, shiny surface with a uniform, even fillet that flows around the connection. It should not be dull, grainy, or have visible gaps, which can indicate insufficient heat or solder. The joint should also have a good mechanical connection, providing strength and stability without any cold joints or cracks. Proper wetting of the surfaces and a consistent amount of solder are key indicators of quality.