So I've had a chance to check things out at the Sheraton D Cube City Hotel, and my general takeaway is that it is a very nice property, despite some not-so-great experiences (of which I do not consider the hotel at-fault, and which I'll go into detail below).
This hotel is located within a building that houses a mall/department store and offices. Because of that, the lobby to the hotel is actually found on the 41st floor, the highest floor of the building. There are dedicated elevators (designated as "Express elevators") to take you from the first floor to the 41st floor, and from the 41st floor there are elevators that service the hotel and guest rooms specifically. The express elevators have stops at the 28th floor (gym/sauna), the 38th floor (club lounge), and the 41st floor (lobby/reception/restaurants/bar).
Upon checking-in at the 41st floor, I was recognized as a Platinum member for my points reservation. I was told by the front desk that I was being upgraded to a corner deluxe room, but NOT a suite. Aventine was right on the money, and my first not-so-great experience is that I did not get upgraded to a suite because they had a lot of people staying at the hotel for staycations (I arrived during a big holiday weekend). I want to make clear that I do not consider the hotel at fault. I am well aware that any suite upgrades would occur on a space-available basis. After being told about the room, I did ask the receptionist if they had a suite available, and they said that I could move to a suite on Sunday evening, if I wanted to. +1 for customer service.
I was of course invited to take advantage of the club lounge as well as the restaurant during the weekdays. The lounge is closed for breakfast during the weekdays, and ALL guests with lounge access are invited take breakfast at the Feast restaurant. During weekends, breakfast is available in the club lounge. For evening cocktails, everything operates normally during the weekdays, but on the weekends you must select one of two sessions. Either 5-630pm or 7-815pm. No pre-reservation for sessions are necessary, whichever session you enter in is the one you pick.
The breakfast offerings in the restaurant are excellent. I saw Japanese, Western, Indian (first time I saw that in a Korean hotel), and of course Korean style breakfast available. Curiously I did not see Chinese-style breakfast (dim-sum/dumplings/etc) offerings. The breakfast offerings in the lounge are also good. It is basically an abbreviated version of the same food from the restaurant.
Evening cocktails have a very nice spread available as well. There were a number of hot food dishes available, as well as a wide variety of snacks. It could be described as a light-medium buffet dinner. Liquor offerings were standard, basically one of everything (Ballantine's, Jameson, Absolut, etc). There were plenty of wines, and they had beer on tap (I think it was Cass) and cans of Premium OB.
Just as an aside, I do wish that the beer offerings were more inspired (I think Korean beer is awful). I also find it curious that no hotel I've visited so far has had signature Korean alcohol like soju or maekgoelli available.
The sauna/gym is included as a Plat member, and it is a similar setup to the Plaza. All-inclusive, including workout clothes, etc. They also have screen-golf available. Actual screen-golf (a golf simulator), not just whacking a ball at mesh. The screen-golf is not included, and costs 10,000KRW per half-hour. The sauna area is very nice, with steam rooms, sauna, hot baths, and a cold bath. They also have a barber available on-site, and offer body scrubs (definitely a unique experience).
The location is definitely outside of the main action in the city. The hotel does sit right on top of the 1 and 2 subway lines, and is connected via a tunnel in the basement directly to the station. It is similarly connected to the mall/department store, where you can find an absolute TON of restaurants/coffee shops. There is also a movie theater available if you want to catch a movie.
Regarding the room itself, the view from the floor-to-ceiling windows are nice, and I found a box of chocolates waiting for me when entering. As far as size, the "deluxe corner room" felt smaller than a regular room, though I think in actuality it is larger in sq ft. I think it's because the bathroom in the deluxe corner room took up a lot of the space.
I actually reserved three rooms on points (my own room, plus two others) at this hotel, to have some family join us for the weekend. I used SNAs on the other two rooms to attempt to get them a suite or a room with lounge access. The SNAs did clear, but I was informed that the rooms they were upgraded to did not include lounge access. Definitely disappointed at this development, and after speaking with the front desk receptionist, they said they would check with a manager to see if we could get access. The manager refused. I then asked if I could cancel the SNAs then, as my main intent was to get lounge access for the guests staying in the extra rooms. They said I could do that by canceling and re-creating the reservation, which I was unable to do in the app. The front-desk receptionists eventually had to call somewhere (I think the reservations line?) to get them cancelled.
I had my points and SNAs returned, and was able to re-create the reservation without using the SNAs.
So this situation was definitely not the fault of the hotel, and they went above and beyond to make me whole, so big props to their customer service.
Overall, I think this property is pretty nice, I just wish it was a bit closer to the center of the city, but if you aren't trying to get in that mix, I think this is a great alternative. It has plenty to do in the surrounding area, and is decently connected if you do find yourself having to go into the city on occasion. Points-wise, it costs the same as the Sheraton Gangnam, which I think is in a much better location, but the Sheraton Gangnam has smaller (regular) rooms.
If anyone is curious about anything else, feel free to ask away. I'm actually still at the hotel, and will be here until Tuesday, when I move to the Sheraton Incheon.