Surprisingly, we don't have a good thread that discusses the relative pros/cons all current Hyatt options in Seoul. So, hopefully this thread can ultimately serve that purpose.
For the OP: here are the master threads for the Hyatt properties in Seoul (no thread exists for SLH Hotel28
Myeongdong):
Park Hyatt Seoul REVIEW - MASTER THREAD
Grand Hyatt Seoul REVIEW - MASTER THREAD
Andaz Seoul REVIEW - MASTER THREAD
-FlyerBeek