Wew that's a doozy of a question and one mountains of books have been written on. There were so many factors to the French Revolution and its "ending" with Napoleon that it's impossible to go through them all, but I'll try a few major ones.

• Basically Terror and Absent Historical Institutions:

The French nation had been rather mismanaged for some time when tensions erupted in 1789. The king and the nobility were visibly and disgustingly wealthy while famines wracked the poorer people who were barely able to scrape by. They get together, overthrow the king, lop off his head etc. etc. etc.

However, France was a nation with an ancient and deeply entrenched history. The people were very accustomed to organizing their lives around exaltation of two things: A monarch and the Church. Suddenly, both of those things are torn down. The problem: What fills the power vacuum?

Everyone has different opinions, they fight to implement their ideas, become paranoid others are trying to stop them, and just about everyone gets executed. As Robespierre famously said "Terror is the order of the day!" It was a deliberate, institutionalized form of terror. Those in charge wanted a message sent to the people, and it certainly worked, but coercion of this sort cannot last indefinitely. The incredible historian Simon Schama wrote in his (highly recommended) book Citizens that, "In some depressingly unavoidable sense, violence was the revolution itself."

Meanwhile, foreign powers declare war on France and pro-Royalist forces in the country rebel. My point here is that the cultural institutions that kept the people in check (the Church and social order) are gone, and so it is a free for all in terms of political order. It is absolute chaos.

After years of this, almost everyone starts looking around and saying, "I really wouldn't mind going through the day without worrying about getting my head chopped off." The people want stability so badly that they don't care where it comes from. When it's a man of rather average height with a slight Italian accent that promises effective leadership, wealth, and a powerful France, they support the hell out of him.

• This outcome is actually rather common throughout history. When things get particularly bad either politically or socially, usually a charismatic man rides in and promises to save the day. Edmund Burke actually anticipated the outcome of the French Revolution years before it devolved into its truly barbaric stages. He wrote:

In the weakness of one kind of authority, and in the fluctuation of all, the officers of an army will remain for some time mutinous and full of faction, until some popular general, who understands the art of conciliating the soldiery, and who possesses the true spirit of command, shall draw the eyes of all men upon himself. Armies will obey him on his personal account. There is no other way of securing military obedience in this state of things. But the moment in which that event shall happen, the person who really commands the army is your master; the master (that is little) of your king, the master of your Assembly, the master of your whole republic.

Amazingly he wrote the book that this excerpt comes from, which is Reflections on the Revolution in France, in 1790, before Louis XVI had even been executed. He anticipated a military dictator because he saw that the people were completely upending the traditional social order and concrete establishments that functioned to keep the country going.

I'm typing this from my phone, so excuse grammar and organization.

The first thing to consider is the insecurity the revolutionary leaders felt. The original intention was to form a constitutional monarchy rather than a republic. However, establishing a new government is hard enough without having a bunch of Austrians trying to reestablish the one you just toppled. This led to a focus on eliminating all threats to the revolution, both internal and external. Once enough heads have rolled people start to feel a little scared for themselves though. This is how the tyranny ultimately ended, but the government's that followed were fairly week. This is where Napoleon comes in. He actually represented a number of ideals that the revolution supported. He wasn't from a rich family and rose through the military ranks based on his charisma and skills rather than any ties to the nobility. France had been at war for nearly ten years when he rose to power as well, so it makes sense that an effective military leader would take control.

To answer the second part of your question, the revolution is celebrated because a number of the reforms lasted after the Borbons took back control and a significant number of the ideals are still around through the implementation of the Napoleonic code.

Lot of good points, and I would point out the Podcast Revolutions for a very in-depth analysis of things.

The French Revolution was in many ways enabled by, and the big little brother of the American revolution. Even it's founding principles - the Rights of Man - was drawn by the "Hero of two worlds" - Lafayette. The problem was that while after the war, left and right in America centralized under the new Constitution and Washington, the French spiraled into increasing radicalism and reactionary cycles, eventually leading to the little Emperor.

France was in a far worse position then the Americans were at the start of the revolution. The state was bankrupt, there was no real middle class, and no history of either religious toleration or participatory democracy. The early French revolution quickly became sensationalized and theater for the masses, with became more and more radicalized thanks to journalists such as Jean-Paul Marat and Jacques Hébert as well as the constant violence from the Sans-culottes.

The French government also inherited a vast amount of debt. to pay that debt, they basically seized the lands of the Catholic church, and sold those lands for a pitance of what it was worth - which basically destroyed the fiscal underpinnings of the highly centralized and planned economy.

This program was later expanded into the forced de-christianization of France. Unlike the United States, where relative religious tolerance and seperation of church and state was a (more or less) established principle before the revolution, the church was viewed as part of the state. When certain parties came to prominence during the parties, they felt that they could replace the Church - with the cult of the supreme being or the cult of reason. This was a factoring leading to war in the vendée, as people didn't like the French government telling them which God to Worship.

All this led to a nasty mess where political parties fought for power, killed their countrymen in the vendee, and then were in turn mowed down as the various winds of current events gave opportunities to opportunists, who could sieze power by being willing to do the things that others ere not.

The failure is celebrated today, but I have always thought that this was misplaced to some degree. Partially this is due to the traditional Euro-centric view of historians. Partially I think it is confusion between the revolution - which ultimately ended in failure, and condemned Europe to another hundred years of wars as monarchs and dictators tried to hold back Democracy with the Declaration of the Rights of Man. Lafayette and Jefferson's Declaration of the Rights of Man and of the Citizen - written before the revolution went brought the same underpinnings to democracy that the declaration of independence, the constitution and the bill of rights brought to America - had the most positive long term and lasting impact on Europe. Even Napoleon for all his faults spread the rights, the way that a pastor would spread the Gospel.