This all depends on what you mean by a Napoleonic World? If you mean a Europe under total French domination, for an indefinite period of time, then it would be a era of intense, periodic coalition wars against France. Even a dismembered Austria would be the strongest German State, and would continue to oppose French hegemony. Rising German Nationalism would become progressively more anti French, spawning new conspiracies, intrigues, and revolts. Britain would continue it maritime, and economic warfare, and finance new coalitions. Russia would continue to spar with France over the fringes of Europe, and interfere with French efforts to consolidate it's control of Germany, and Italy, sometimes working with, and sometimes against the British.
If you mean an Imperial France far larger, and more powerful then the OTL France before, or after the Revolutionary, and Napoleonic wars that has better possibilities. If say the Peace of Amiens becomes a semi permeant arrangement France could could be much more powerful then in the OTL. Belgium, and the Rhineland could be part of France. A buffer zone of minor German States could be led by France, with an Austrian Alliance that would prevent the unification of Germany has we know it, under Prussia. Most of mainland Italy could be dominated by France, preventing the OTL unification of Italy.
Instead of a 20th Century shaped by the rise of Germany, and it's attempts to impose it's hegemony over Europe, it could be a century of continued imperial conflicts between the UK & France. If France attempted to claim Louisiana it would find itself in long term conflicts with the United States. This would force the USA into joining in coalition wars against France, pushing the Anglo/Saxon Powers into each others arms. The Great Powers in 2021 could Be the UK & Commonwealth, USA, France, the Constitutional Russian Empire, Nationalist China, India, and Japan.
Without the rise of Germany, and Italy as unified nation States the world would move in different, and unpredictable directions. Without the chaos of WWI the collectivist monster States of the 20th Century might never come into being, and their destructive ideologies might die stillborn. The world would be no paradise, but it might have been spared some of the massive tragedies of the last 100 years.