Sakon Nakhon is hardly the heart of Isaan. It's right up in the North East of the region.
Isaan food is great.
You didn't say what food you are looking for. I guess Western Food. In which case you can add Surin, Sissaket, Nong Khai, Ubon, Buriram, Roiet, Kalasin, Mukdahan to your list.