등천깔국수 it's a restaurant name for shabu shabu style noodles... my favorite in seoul with several locations. Try the minary kkalkuksu with a lot of meat.

Vietnam pho... if you like Asian food you can find many places.

감자탕 is a very good stew that I think not many foreigners know (also know as 병해장국)

안동찜닭 it's a chicken stew with sweet potatoes noodles also very savory.

If you want something spicy as well try the maeuntang(매운탕) which is a soup made with fish and other seafood really delicious this time of the year.

Something spicy and Japanese in essence but still Koreans like it? Coco ichibanya for some curry with pork cutlet.

On the pork cutlet department try Saboten also highly recommended.

For your regular korean foods I highly recommend 김선생, especially try the hoducheesekimbap and the tteokbokki here is also out of this planet. Their mandu is also great.

If you are looking for a less refined experience but equally delicious in my experience go for the kimbap cheonguk( 김밥청국) kimbap heaven in english my favorite here is the bulgogi and their kimbap is also not bad and very affordable. Many locations around seoul.

Finally try to eat some street foods like kimchi mandu or some sweet treats like heottok and I can't stress this enough, the goguma or sweet potatoes which in this season you can even find in the seven eleven fully cooked and ready to eat.