He was taught to me as a generally good emperor, known for presiding over the voyages of Zheng He. Years later, I get curious, and do some research. Emperor Yongle's entire wikipedia page seems to be concerned with his rise to power, overthrowing his nephew, the choice of his father for emperor. What gives? And is his legacy viewed differently in China versus the rest of the world, which seems to care mostly about those Zheng He voyages?
He is an interesting case, and worth considering. The usurpation is a big part of who he was, and of what he did with his reign. It was a bloody, merciless affair, that left the rightful emperor, Zhu Di's nephew, dead (or forever lost to some mountain monastery!). The end of the rebellion also saw the execution of many of the finest scholars of the day, and their families. So, he didn't start well... and it makes sense to look at the ostentatious displays that characterize his reign as part of an exhaustive effort to vindicate himself and legitimize his reign. These were:
So, in terms of material accomplishments, Zhu Di is unparalleled in the history of Chinese emperors. He cuts an imposing and astonishing figure in the annals of History, and must be considered great when looked at from the material culture lens.
However, lets look at his overall effectiveness and legacy:
He emptied the imperial coffers on his many expensive projects, and none of them increased revenue for the government. The treasure fleet's journeys were great for chinese traders, who had a massive navy to give them safe passage to and from the indian ocean trade ports, but their trading continued relatively unabated after the imperial fleets were grounded. So, any money made from trade was overwhelmingly made by traders and not by the government, who's voyages were designed to establish unequal trade. Meaning - the trade partners were never going to be able to match the "gifts" of the treasure ships, and so would be stuck in permanent trade deficit (again - today's pattern, established 600 years ago!). The problem is that every accountant who looked at imperial books saw this was completely unsustainable. So, the great secret as to why the fleets stopped their incredible journeys turns out to be pretty dull: they were too expensive.
There is another reason the fleets stopped running: the canal was revitalized and fully operational by the 1420's - so all the trade that the mongols and the early ming governments were managing in the East China Sea was diverted back to the internal canal route. Mote (rightly, I think) points out that this was not a great long term move. Sea trade was faster, and generally more reliable, but could occasionally be subject to pirate disruption (hence the navy, Zheng He, etc...) and catastrophic weather disturbances. Nonetheless, it would likely have paid more in the long term to stay in the sea. The Canal was notoriously fussy, and constantly in disrepair, not because of negligence, but because the climate was (and is) so volatile, flooding is the norm.
So, his legacy was poor economically. Militarily, he was an astute manager of the Mongol threat to the north. The moving of the capital to Beijing represents a seismic shift in Chinese geo-politics, according to Mark Edward Lewis (in a paper he gave at a conference a few years back) from that of rule from the core, to peripheral rule, primarily focused on the land-based threat of the northern nomads.
This worked well in dealing with the Mongols, but combined with the removal of the navy and reduction of sea trade, this also left the Ming open to incursion from the dwarf pirates (putatively, but not all that often actually Japanese), and later, from the Europeans.
But, Zhu Di's move to silver also opened the doors to immense wealth from the same Europeans. When the spanish found their Silver mountain in the 16th century, this opened up the flood of silver into and goods out of China. So Zhu Di's legacy (though he could not predict the future) is wrapped up in the enriching of his and the next Dynasty via spanish silver.
Nonetheless, without naval advancements, ultimately the Chinese would be too vulnerable. This didn't become a problem until the 1840's (the british were still unable to effectively control chinese trade until the success of the first Opium war, until then, no europeans could dictate trade conditions, because none could effectively fight off the Chinese for the right to do so - see the portuguese failures of the 16th century, dutch failures of the 17th in Taiwan, and british struggles in the early 19th century, even as late as the 1830's - when they were unable to subdue chinese forces in the Yangze) when the British finally established military dominance over the Qing.
So, in this long term example, Zhu Di's legacy is less positive. But again, he could not have known the ultimate import of either silver or the reduction of the navy. In fact, he didn't even foresee the wholesale reduction of the navy that the canal's renovation made inevitable.
The last element of his legacy is his (slightly) premature death - many projects were incomplete. The fleets were away, the tombs half-finished. The response was swift - a pretty intense backlash soon followed, and the government went into a more austere mode.
One last element of his legacy which is questionable - his raising of the status and importance of Eunuchs sowed the seeds of Eunuch power and misbehavior down the line. Eunuchs were often at the heart of political disasters and malfeasances from the time of Zhu Di until the end of the dynastic period in 1911. Much of the precedent for their power and positions in government starts with Zhu Di.
What then of his legacy? It's complicated!