I have stayed here a few times and it's one of the best Conrads I have been to. The hardware is fantastic and is one of the few hotels that I consistently book a suite to guarantee that I will have one (rather than hope for an upgrade), because it is a great room. If you are patient and if you can forego the flexibility of travel dates, and you are willing to lock yourself into prepaid rates, then you can usually wait for a flash sale and get the suite for a very good price. Last time I booked months in advance and I got the suite for 2.3m KRW per night, so 210 USD. And about a couple months before my stay, I saw another flash sale where I could have paid about 10% less so sub $200 for a suite which is amazing. During my last stay, the weather was getting cold and the heating system in the room started kicking in, and was making a bit of clicking noise and I could not sleep. They temporarily transferred me to another room just for the night to sleep (and I could leave all my belongings in the suite). I therefore could see how the standard rooms look like, and they are great as well. Very spacious and the bathroom while not as impressive as in the suites, still one of the better ones I have seen for a standard room.
Conrad Seoul is also one of the very few hotels where I do not shop to compare with the competition because I find that what I get is top notch for a good price and I am fully satisfied. Almost everywhere else in the world I like to mix things up to see what's on offer in other hotels. That by itself is the most telling fact about my opinion of the Conrad.
I usually like a quiet breakfast in the lounge, but at this hotel the breakfast in the restaurant is so great that I always eat there, and never in the lounge. The gym is excellent and has a nice choice of machines. You can easily access the hotel from the airport door to door with the airport bus
#6030 for 15k KRW per person.
One of the few downsides is as mentioned by others in this thread. The executive lounge on weekends feels like a completely different place than during the week. It is full of people on a staycation, very busy and very crowded; not nearly as enjoyable. In addition, I have found the food quality in the lounge for happy hour to be decreasing in the last couple of years, particularly the choice of warm food. They have three options and nowadays is typically fried stuff and sometimes pizza, whereas they used to have more elaborate dishes that you could turn into a meal. It's a bit of a disappointment for Asian standards, but the hotel being connected to the IFC mall which has a food court, you can easily have several choices for dinner without having to go outside, and you also have several options to bring back takeaway when in the mood for eating in the room to enjoy the suite. I have done it on several occasions.
The hotel is connected to Seoul Metro lines 5 and 9 via the underground through the IFC mall. It is convenient but a bit of a walk before getting to the station. Which brings me to the other slight negative about the Conrad. For several places we want to go to, lines 5 and 9 are actually not the most convenient for us, for example if you want to go to Myeongdong which is not that far from Yeouido, yet you have to change lines twice. Also the line transfers in the Seoul metro system is not always straightforward like it is in other cities. There can be a long walk between lines within the same station. So you end up sometimes being better off just transferring once and walk the rest of the way to your destination, rather than transferring lines twice to reach the station exactly at the destination you want to be. Anyway, all that to say that if you are not in Seoul for business, perhaps Yeouido is not the best location. The metro will bring you where you need to be, but expect that it might take a bit longer than you think. Not nearly a deal killer for me but if you have never been to Seoul and will go for only 2-3 days and want to maximize your time, you should keep that in mind.