Thought I would add a few more comments after Ferrismo's great review of the GH Seoul. Overall, a great hotel with very nice staff and personally had a fantastic stay. The whole hotel is in great shape and the rooms have been kept nicely. If you want the bottom line and are trying to decide between GH and PH, on business choose PH, with family choose GH.
I also disagree also with some of the comments before mentioning that GH is far from anything. You should be able to get to a lot of attractions by taxi for less than $10. Closer ones like Itaewon, Namsan Cable car for less than 5. Taxi fare is extremely cheap and there seemed to be always a cab in front of the GH every time we were going somewhere.
Inside the hotel, we had free access to the pool/fitness center and spa facilities and I would recommend GH over PH if you have kids since the PH does not let kids under 16 into the pool/fitness room/spa. There are 3 swimming pools at the GH, one indoors and 2 outdoors with a kiddie pool as well. The larger pools are also accessible by kids and there are lifeguards in the bigger pools. For those of you seeking space from the noise of the kids, there is a separate area for sunbathing near the waterfalls. Outside pools close at 6 PM and the indoor one closes at 9:30 PM.
The fitness club was nice and so was the spa, but the spa is closed on Mondays for maintenance-not sure if this was just the first Monday of each month or every Monday. If you are into tennis there are 3 grass courts that can be rented each for KRW27000/hr.
Club room service was great. Great food and great drinks. Free alcoholic drinks -wine, beer, scotch and champaign. Saw quite a few happy people there.
A few comments about the rooms. I had used points and was given a "Grand King" with the reservation. Upon arrival, I was taken to the 17th floor check in counter due to my "VIP" status-I believe they were referring the diamond status. The room I was given was the "Club View King" and when I tried to negotiate a suite, the receptionist kept insisting that I use my upgrade for other future stays. She seemed surprised when I told her that diamonds get upgraded rather frequently to suites in the US without the use of the free upgrades. Oh, well, I was not expecting too much since this stay was not a paid stay anyway. She also mentioned something about using 18000 points per night to be upgraded to a suite, perhaps indicating that they will only upgrade you once even if you are a diamond member.
One thing I noticed later is that GH Seoul has the cheaper "Grand Deluxe King" rooms, that are much bigger 45 sqm and nicer (by looking at the pictures). They do not have the view of the Han river, but you can get the view from the club lounge anyway. Also thought the extra money they charge for the view is not really worth it if turns out to be a smoggy day. It may be worth it to book this room and just ask for access to the club lounge with the diamond upgrade if there are no suites available.
Overall, a great hotel, but will stay at the PH in a heartbeat if I was on business.