I took a bus from Bankok to Siem Riep, then a speedboat to Phnom Phen and a prop plane to Ratanakiri in the NE
It was a REALLY bad road - shakes you non-stop the whole time once you pass through into the country. there’s a good chance it’s like that from the other direction as well
The border itself wasn’t bad and we bought the visa on the spot without problems. It was interesting to see the country that way, but in hindsight it probably would have been better to just fly
You can take a speedboat up the Tong Lee Sap between PP and SR and it’s nice and sunny, but everyone says not to go inside the overcrowded boats in case they sink! We drove the same journey and the road was too shakey
Ankor Wat is great once you get there, especially the temples still overgrown in the jungle. Have fun!