Isaan is pretty flat thus its not a lot of twisties to be found there like in the north. At least when youre east of Loei, Chaiaphum and Petchabun provinces.
I crossed Isaan a few times and riding wise its not very inspiring. The only road I have enjoyed a bit is when following the Mekong south and east from Nong Khai and via Bueng Kan - Nakhon Phanom - That Phanom - Mukdahan - Amnat Charoen and keep east of the Sirinthorn lake before turning westbound again.
Like a continuation of the stretch R211 Chiang Khan - Nong Khai you can say.
Any sights along the way,
The Erawan cave along the R210 on the border between Lowi and Nong Bua Lamphu. A cave that goes completely through a carst mountain, accesibel by foot but prepare to sweat a little.
In Nong Khai: Sala Kheow Ku - the sculpture park - I think I saw you visited the sculpture park on the Lao side, this is made by the same man only at a later stage in life when he moved to the opposite side of Mekong. His body is on display on the third floor btw.
Nong Khai aquarium - not the most impressing aquarium, but still worth an hour of visit. There are many huge «pla beuks» there.
Nakhon Phanom - a plaesant Mekong provincial capital. Visit Ho Chi Minh old house and Indochina market.
That Phanom - is where one of the most important buddist shrines in Thailand are placed - Wat That Phanom.
In southern Isaan:
Old Khmer style temples are plentiful there. The best preserved is Ka Phanom Rung in Buriram province, a bit west of the town of Prakhon Chai along R24.
Another good one is situated in Phimai a bit north of Korat along R206. The temple ruins are situated just in the city center.
Khao Preah Viharn - actually in Cambodia but easiest acsess is from Thailand in Si Sakhet province. I dont know if its open for the moment, better check it out before a planned visit.
Just a few places that I know about and have visited. There are many more for sure...
