It's a good location, but IMO the Plaza is just an aging large ugly modern hotel and doesn't appear to be anything special, but I've only walked through the lobby and have never stayed there. However, my impression is that it focuses on Korean guests and is held in high regard by them. I was surprised when it affiliated with Marriott and I'm also somewhat surprised that it would have a corporate rate with a major international company.

Does the OP know whether the corporate rate predates the Marriott affiliation or is part of some larger Marriott corporate contract?