Honestly, barring our mosquito issue, this hotel would have received a 4/5 review from me--for the price, it's fine, although it could be a little cleaner. However, our window did not close all the way. This wasn't an issue for temperature, as it wasn't too cold yet in late October. However, I noticed a few mosquitos the second night. Even though I put on bug spray that night, I found 10 bug bites in areas I missed, or in places where the mosquitos had bitten before I applied bug spray (three of which were on my face!). My partner, who declined the bug spray, fared much worse. He awoke with 20 or so bug bites...
I know this can't be the first time a traveler has been bitten in that room, because I found a smushed mosquito corpse on the wall, and the bed sheet had a small blood stain on it.
I notified the staff, and hopefully they will address the issue. I'm a little skeptical--they were apologetic, but didn't say they would take action--but let's give them the benefit of the doubt.
Advice: if you are going to stay at the WS Sinchon, carefully inspect your room upon arrival. If you see an unclose-able and unscreened window and/or evidence of mosquitos, ask to be relocated to a different room. If they refuse, feel free to site this review, ask for a refund, and go to a different hotel! I wish we had noticed when we first checked in.