A trip on the Thai-Burma Railway is well worth your time! If possible, visit the museum and the graveyards in town first so that you can understand the history of the railway and the terrible loss of life in building this system. The museum, small, is very well done with good signage to help you understand the process of construction and the roles of those from many countries who built it.
The ride itself is fun. Sit on the left hand side if you can so you can get the best views. Different vendors will come through the train selling snacks. Sit with the locals. Avoid the extra charge of the tourist car. You'll have more fun with everyone sitting on the harder seats.