Considering that the Kaiserreich went to war in 1914 in the hopes of becoming a world power, I would say the Nazi Germany was not. It's Navy could not hope to match Britain, and was badly damaged after the Norway campaign. Neither the U-Boat Campaign nor the Luftwaffe's air campaign against Britain came close enough to defeating Britain, and with the addition of the United States and USSR to the Alliance, Nazi Germany was doomed.

On the Ground, the Heer was able to pull off stunning successes up to the Operational level, but strategically the Third Reich was in dire straits. By 1941, German fuel reserves were running low, and the Third Reich was essentially forced to plunder it's occupied territories to make ends meet. The culmination of this was the Invasion of the Soviet Union, which was tactically a success, but strategically disastrous. The Germans were at war by 1942, with the World's greatest Land Power, greatest Naval Power, and the upcoming superpower. Defeat was already pretty much certain, it was simply a matter of convincing the Germans that this was the case; no easy task!

At best, the Third Reich at it's greatest territorial extent (c. summer, 1942) could claim GREAT power status, like the Kaiserreich in 1914, but by this time it's days were already numbered.

For an idea of the economics of the Reich, Adam Tooze's Wages of Destruction is excellent. For a good general history of the war, I'd recommend Max Hastings's All Hell Let Loose.

There are two ways to measure Nazi power. In terms of raw military might in comparison to its enemies, its peak could be said to have occurred after the conquest of France in June 1940 and a weakened Britain stood alone against Hitler.

A second way is in terms of its territorial expansion in 1942, when Germany's conquests extended from the Pyrenees to the Caucusus from east to west and from the Arctic Circle to North Africa from north to south.

At its first peak, in 1940, it is indeed possible that Germany was the most "powerful" nation on earth. The United States was unprepared for war, Britain was desperately attempting to rebuild its armed forces in case of invasion and even though the Soviet Union's air force was bigger than the rest of the world's combined at that time and its army was as big as the rest of the world's combined, it was still recovering from Stalin's Blood Purge of the officer corps.

At its "second peak" in 1942, the awakening United States and a recovering Britain would have made such a claim much more difficult to make, while the Soviets were still in the process of refining the Red Army into the juggernaut of 1944-45 that we all know.

The Germans were certainly a very strong regional power dominating most of Europe, and much of the Mediterranean region. That said, while they did have the ability to effect shipping in the Atlantic; they could never have put together enough men to invade North America. So I would say that, yes at it's peak Germany was a world power. But it was never the most powerful. America especially, and even the UK, had some big advantages over it in terms of influence far from their own militaries as well as colonies.