Stayed at Lavinia for six nights, and I found it to be in a very convenient location. A subway station minutes away (with a small Korean royal palace with free admission along the way to visit), a convenience store and various eateries nearby, and of course, a lot of major tourist spots (Insadong, Myeongdong, various Korean palaces) within walking distance or within a few subway stops away.
Travel to and from Incheon International Airport is simple enough, as there is an Airport Limousine Bus that goes to the subway station nearby, and can be taken back to the airport as well. If you're not carrying much and wanna save money, you can take the subway as well.
The room I had was pretty clean, but for some reason, had no bedsheets, just some covers. And there was what looked to be a tiny spot of dried blood on the bed. Elsewhere, the dresser table had a leg that looked like it would snap off soon, and the bathroom had an odd smell at times. These are the only negatives I found however, as in terms of service, they were great, and I actually found it a comfortable stay despite the little hiccups. Room was a little small, but most hotel rooms in Seoul are like that. For a solo traveller, it was no problem.
Fresh towels (relatively small in size) delivered everyday, along with complimentary bottles of water too. Body wash/soap is provided, but bring your own toiletries otherwise. There are cable channels and free Wifi to entertain yourself with in the room, and a small mini-fridge to chill things in.
I noticed that almost all the guests I came across while I was staying there were quite young (and were female and mostly spoke either Chinese or Japanese), and I would recommend this place mainly for young travellers, whether solo, a couple or in a group. The flaws I pointed out are minor to me, but likely to be annoying to older people (from my own experience, at least). The space is likely to be too small for families and those fond of carrying large luggage. Would add that there is no wardrobe for hanging clothing, you just get some sort of coat/hat rack with three hangers for that. Not an issue for me, but again, I find older folks care about this.
In short, great for young people, not for families or people who want a low price but expect perfection.