The nature of the occupation depends upon what point of Japanese rule you look at since it changed from inception in 1910 to its conclusion in 1945. At all points during the occupation, however, the Japanese ran a top-down, highly centralized military operation in Korea. The administration of the colonial rule in Korea was entrusted to a governor general who was appointed by the emperor and was almost always a general or an admiral. Beneath this man was a complex system that managed the colony which consisted of approximately 300,000 people (soldiers, government officials, private companies) and more than 75% of these were Japanese.

The first decade of rule was harsh. The Japanese ran things like a military operation and the governor general made wide use of his near-dictatorial power. The press was heavily limited and regulated by the Japanese authorities. Any assembly of any kind had to have a police permit, and all political gatherings were outlawed. Political gatherings that did occur could be suppressed with violence as was the case in the March 1 Movement. Furthermore, the Japanese did not shy away from using the police force to suppress anti-colonial forces.

After the end of the WWI the condition in Korea improved. Many of the restrictions that had been placed on Koreans were lightened. Some press restrictions were lifted, Japanese civil servants no longer carried swords as a status symbol, Koreans began to receive the same pay as Japanese employees, and the military-like police force was changed for a civilian force. Koreans were still not allowed to advocate for independence, but the Japanese took on a more liberal stance from the end of WWI until 1930. This liberal stance is most likely due to the March 1 Movement, which was a national embarrassment for the Japanese, and a desire to bring themselves closer to the democratically minded victors of WWI (USA, Britain, etc.)

This, however, did not last. In the 1930s Japan began to mobilize for wartime which drastically changed the situation in Korea. In order to meet the demand for labor needs in the factories Koreans were forcibly moved out of the countryside and into the cities. All Korean organizations were disbanded and replaced with military minded Japanese organizations. By 1943 enlistment in the Japanese army became mandatory for Koreans. Additionally, the Japanese took the step of attempting to assimilate Korea into Japanese culture by force. All Koreans were forced to register at Shinto Shrines and participate in Shinto worship ceremonies. Additionally, Koreans were forced to abandon their Korean names and take on Japanese names. Finally, the use of Korean in any publication was banned. All Korean newspapers, magazines, and books had to immediately cease production. They were replaced by newspapers, magazines, and books written entirely in Japanese.

The wartime period also coincides with the use of comfort women by the Japanese military. These women were overwhelmingly Korean and were lured away from their homes with promises of a happy life and good paying jobs. In reality, the Japanese military abused them and forced them to serve as sex slaves for their soldiers. There are reports of some of these women being forced to have sex with Japanese soldiers over thirty times per day. Many died as a result of their abuse. Some committed suicide. It's still a very contentious issue between the Japanese and the Koreans today since many Koreans believe that the Japanese haven't sufficiently apologized for this abuse.

tl;dr version - It changed depending on the time. 1910-1918 was a lot of political oppression. 1918-1930 saw a more liberal policy. 1930-1945 was harsh and cruel.