Maybe someone can answer this but what is the conditions like of the average citizen/civilian on Earth in Halo during these times? Are people generally oppressed, poor and diseased or are they generally well off like in Mass Effect or Star Trek?
It's more like Mass Effect than Star Trek, except no aliens.
Humanity set up some some colonies around our solar system. Mars, our Moon and a few other places. We had some bickering and disagreements, some serious conflicts during this time, typical humanity. We discovered FTL and spread out further. More colonies. With new planets and such the bulk of humanity migrated from Earth.
Mass migration and colonisation, politics and yup, more war. This time, with such vast distances from Earth, political discontent was inevitable, particularly due to the concentration and prosperity of the worlds closer to Earth and the difficulties of the frontier colonies.
Just before the Covenant War, there was a significant Insurrectionist movement against the main governing political body, the UNSC. The insurrection was a serious military threat for the UNSC with the proliferation of nuclear weapons and other technologies. The UNSC determined that humanity was at risk of self-annihilation so they clamped down hard. The Insurrectionists fought back harder.
The SPARTAN-II project and the Spartans was the solution to this problem and their deployment against the Insurrection was initially successful. It's entirely possible that the Spartans could have eliminated the entire Insurrection threat and saved billions of lives by pre-maturely ending the conflict.
The the Covenant was discovered. Entire planets fell silent, never to be heard from again. This sudden and unusual interruption halted the action against the Insurrection momentarily. As the Human-Covenant war progressed, the Insurrectionists tried to use the opportunity. Even up to the fall of Reach, the Insurrectionists were still fighting against the UNSC even though the humanity was facing mass genocide.
The UNSC and the Insurrectionists stopped paying attention to one another. The UNSC abandoned the Insurrectionists and retreated the remaining human population to Reach, Earth and the core inner worlds (colonies closer to Earth). It was assumed the Insurrection died when their home colonies went dark and communications ceased as the Covenant invaded.
Even with all the conflict, the majority of people were trying to get on with their lives. Gardeners, teachers, housewives, shop keepers, vehicle manufacturers. A lot of folks lost their homes and families but everyone struggled onwards. When the UNSC was pushed back to Earth and all the colonies feared lost, again, the survivors continued on trying to live normal lives. There was no mass panic, no breakdown of government.
After the Human-Covenant war? Well that story is still being written.