Just back from 3 days 2 nights driving from Ayutthaya to Nongkhai and into Vientiane for 4 hours only. Several interesting stops along the way, including a stop to see my niece Nok and her husband Mon in the small city of Muang Phol, Khon Kaen. We actually spent most of 2 days sitting in the van, traveling, but still managed to see some nice sights and saw the scenery on the 600+ km stretch between home and Nongkhai.
As you climb up from nearby Saraburi onto the Korat Plateau, the weather becomes cooler in the morning and hotter in the daytime. Once you're past Nakorn Ratchasima (Korat), it becomes much drier, as evidenced by the much less green shrubbery and fields, compared to Central Thailand. It seems Isaan (NE Thailand) is rather dry, and not at all lush. Actually it's like parts of Southern California.
Nongkhai really feels like a border town, crawling with transients from all nations, many Farangs heading for Laos, yet a lot of residents. It sits on the beautiful River Khong (Mekong as we know if from further downstream during the Vietnam War). Nice setting.
I don't think 4 hours in Laos qualifies me as an expert, but here are some observations: the people look Thai; the food tastes like Thai; but Vientiane looks NOTHING like Thailand. Despite being at a lower level of development than any Thai city, and not as clean as Thailand, it really feels like the French left their mark. The city doesn't have the kind of random feel that Thai cities do. Vientiane, though seemingly not so large, looks more like what we Westerners consider a "city". Facebook friends or those who got my Kodak link will get a look. I hope to go back and take another, longer look, as well as explore Isan.
Oh, and make sure you can count high in Lao if you go there: 250 Lao kip = 1 thai baht = 3.3 US Cents. So lunch for four is.... well, you do the math. They accept Thai baht happily and will give change in Baht, except at small stands where you get change in Kip. Need to go back and spend more kip.