Splitting this into two replies...
In the popular press dopamine was known as the pleasure or reward neurotransmitter because of its associating with drug addition but with new research that view is slowly changing. While drugs like cocaine or meth produce euphoria research has also shown that dopamine is also released in response to unpleasant stimuli like stubbing your toe or the near miss at the roulette table. My view, which is shared by some researchers, is that dopamine is primarily involved with the salience, or whats important, about an object or situation.
For example, walking down the street the sudden appearance of an aggressive dog or stumbling on gold coin would trigger the release of dopamine and norepinephrine. The release signals to the rest of the brain that something important has happened and to pay attention (focus). The release also simulates memory formation and learning and it makes us slightly less empathetic. It also deactivates sensory suppression and makes us more aware of our surroundings and puts puts movements on a hair trigger. All of which probably facilitates survival.
However in my case the compromised ability to break down dopamine and norepinephrine via the COMT pathway left that system always on. While this contributed to some of my strengths only retrospectively do I now recognize that there were downsides. Enhanced memory formation and learning also means never forgetting and intrusive thoughts in vivid detail an awkward social situation a decade ago. Heightened sensory awareness means that you can't filter out somebody tapping in the next cube or unfamiliar clothing. Twitch like reflexes compromise fine motor skills (like handwriting). And while reduced empathy can help slice through the politics to "do the right thing" it is pretty much a downer in every other way.
Looking back there are also some other things that I can now see with more clarity. I believe that the brain uses the relative levels of tonic dopamine versus tonic serotonin to measure the levels of wanting (or desire) versus getting (or consummation) which I think is the brains proxy for social status. My compromised COMT pathways resulted in my perception of always being subordinate in any work or social situation. Other than the obvious it has some other subtle side effects including an exaggerated sense of justice and rapid escalation of a perceived threat. This seriously hampered career advancement for a long time because it ruled out a leadership role to other people.