3rd class was better than expected! Very comfy seats, just a bit narrow. Little delay, but overall very good experience. Felt exhausted after a 14hrs ride, but that's normal. People selling food and drinks on a regular basis. Toilet was very clean! Overall a very good, but long experience!
Well it is worth the money - 8 dollars or so that we paid. Many people - tourists and locals travel together. Don't worry about food or drinks - locals are selling food on train all the time. Toilets are ok. Seats ok, well not too much space but managable, everythone gets dedicated seat. Just be sure you are ok to travel so long, like 14 hours! And bring a jacket, it's cold and windy in the early morning, most windows and doors usually open all the time.
The toilets were terrible, we also had a upper bed which I can not recommend as a tall person, also the train was delayed for 45min, for people whith further connections it could be a problem. The new train which we had from bangkok to chiang mai is better.
Easy to reach the tickets. We were 4 People and we wanted to travel in 1st class and they made us a reservation for two communicated cabins for being the four together.
Train was comfortable and only 30 minutes late into Hua Lamphong station.
Train was newer and very clean. AC was on full, so advise having a sweater or extra blanket on hand.