I see lots of cold solder joints. Here's an image of a good joint next to one that likely won't work. If the solder doesn't flow all the way through the plated through hole, then you an assume that the flux in the solder has floated to the surface and is stuck between the solder and the component lead, acting as an insulator.
On parts like resistors and transistors, they can take a fair amount of heat to properly solder (LEDs and capacitors tend not to take so much heat). The MJE5731A, for example, may need 5-10 seconds of iron heat on the middle leg to allow for the solder to flow properly.
-PB