This is not just some Forbidden City
I've read and heard a lot of people comparing the Gyeongbukgung and the other Korean palaces to China's Forbidden City. In fact, most of Korea's historical architecture has been compared to China's. Well, don't be fooled. Come to any of Korea's historical structures, Gyeongbukgung being one of the best, and you'll see and feel the difference. I also recommend the Changdeokgung Palace if you're in Seoul, but go to Gyeongbukgung first.
Unlike the Forbidden City, Korean palaces are much more like temples than like those large, majestic quarters of kings and emperors. If you notice the color scheme, the jade greens, faded reds, etc., you'd notice the buildings' almost eyebrow-raising impression on you. It calms the open-minded onlooker, unlike the Forbidden Palace or even the Imperial Castle of Tokyo, which are built to impress and intimidate.
Instead, Korea's architecture tries to work with nature. So I suggest you visit Korea in early autumn to understand what I mean. The mixes of greens, reds, and yellows of the mountain trees, matches perfectly with the colors on the palaces.
I recommend you go to Gyeongbokgung before Changdeokgung because, well, Gyeongbokgung is true seat of the Joseon Dynasty, built to be the heart of Confucianism. The almost perfect balance of the Gyeongbokgung palace does not fail to impress. The Changdeokgung, on the other hand, gives almost an explanation to a tourist of Korea's uniqueness. It will make a beautiful last impression. Go to the Biwon "Secret" Garden of the Changdeokgung, look at how Koreans "built" their gardens. See how little they touched nature and how they added their own Korean touch with buildings and ponds.
You will see the beauty of Korea's seemingly small, subtle architecture in Gyeongbokgung and Changdeokgung. Then, you will realize comparing Korean palaces with China's is just ridiculous.
Enjoy!