One thing you should be aware of, when discussing the Napoleonic conquests, is that the Wars of the Coalition ultimately predate Napoleon himself (in fact, Napoleon largely made his reputation as a Revolutionary general serving in Italy). Indeed, the Wars of Coalition can be understood, at least in part, as an existential struggle between two political systems that would not co-exist: either the Revolution would prove victorious, or it would be crushed. From that perspective, while we certainly should not overlook Napoleon's own aggression and drive towards domination, we should also recognize that that the expansion of French hegemony was (at least in some part) an attempt to stabilize and secure the Revolutionary (and post-Revolutionary) system.

As important as the conquests themselves are, however, it is just as important to keep in mind what Napoleon achieved as an administrator of empire. Entire countries were created in Bonaparte's wake, and the political maps of Europe were withdrawn. We see this in his support of the Sister Republics, as well as in his reorganization and consolidation of the Holy Roman Empire into the Confederation of the Rhine. Additionally, he rewrote political systems throughout Europe, instituting Constitutional governments, and installing close allies and family members as Heads of State. In this manner, he was able to expand Constitutional principles throughout Europe, as well as to further secure the position of France, and expand his own hegemony and power within Europe.

That being said, there were several critical failures that contributed to his downfall. For one thing, even though he conquered Spain, he was unable to truly secure it, as Spain broke out in large scale revolt and unrest (it's from this context that we get the word "guerilla warfare"). This served as a near continuous distraction, which Napoleon was never able to solve. In addition, there is the specter of Britain itself, which Napoleon was never able to solve. Between its naval power (which gave it a considerable ability to blockade and weaken the French economy) and its economic strength, by which it was able to monetarily support its allies on the Continent, Britain was an enemy that could do considerable damage to Napoleon's empire, and one he was hard pressed to defeat. Napoleon's response to this challenge was to eventually institute the Continental System, by which he attempted to exert economic pressure on his enemy, by closing all ports within the Empire to British ships. Finally, there was his disastrous invasion of Russia, which did much to shape his defeat.

Napoleon was (in)famous for his aggressive military strategies; Napoleon's foreign policies were of military and economic aggression. Napoleon sought to create an empire under his rule in Europe. His plan involved isolating Great Britain through the Continental Blockade, in which Great Britain was to be cut off from accessing economic trade with France, French allies, and neutral countries. Napoleon's plan was to cripple Great Britain and then proceed in bringing the rest of Europe under his control. Napoleon also sought to maintain power over several French colonies. However, the powerful and successful uprising of enslaved Haitians led to Napoleon deciding to focus more on conquering Europe than controlling distant colonies. Napoleon's ridiculous military invasion of Russia in 1812 ultimately led to his downfall.

While the first answer sees Napoleon in a very negative and predatory way, I think that you can argue that Napoleon's foreign policies were not the way he characterizes them (or not completely, at least).

Napoleon was trying to spread the ideas of the French Revolution, in my opinion.  You can see that he was doing this by the fact that he imposed the values of that revolution in every country that he conquered.

This is one reason why the rest of Europe was arrayed against him.  They saw him as a threat to the stability of their countries and their social systems.

You mean besides conquering everything in sight?  Outside of literally working to bring the whole of Europe under his rule, Napoleon generally used any means he could, including his relatives, marriage to key royalty in other countries, and threats to manage his neighbors and allies.

One notable policy of Napoleons was the re-institution of slavery in the French colonies and subsequently was defeated in Haiti as his expeditionary force was unable to contend with an army of slaves.  This, some speculate, led him to decide that trying to maintain some of these colonies was not worth the expense and he then looked favorably upon the sale of the Louisiana Purchase to the United States.