About two years ago, I did the train from the Sentral KL station to Butterworth; "first class", but prior to the new ETS trains. It was an experience going through the Malaysian countryside. The issue is that I arrived in Butterworth after dark and there was some question about the ferry schedule. I would have had to walk from the Butterworth station, to the ferry landing, basically in the dark; so I chose a taxi instead. The taxi ride to Georgetown was lengthy and relatively expensive.

Also, I thought that I'd make the return trip. I took the ferry to the train station (during the day) to buy a return ticket two days in advance and the train was sold out, both first and second class, for something like 4 days. I ended up using Air Asia to return to KL.

That said, the train station in Butterworth is brand new and it appeared that the train system was upping its game - hence the new ETS trains.

Just know how you'll get from Butterworth to Georgetown upon arrival.

(I do recall something about the ability to take the train from Singapore to Butterworth with a quick stop at the border.)