My son loves trains so this is perfect for him. One of his favorite things to do is make the train repeat the word, over and over and over again. He also likes to touch each letter repeatedly to hear the sound each letter says. He has known his letters and sounds for a while now and he still finds this engaging.
That said, I'd like to see two changes. First, could the engine say the word and the individual cars say the sound? We talk about isolating the sounds of CVC words. For example, "What is the first sound you hear?" I think it would be nice to have a way for the player to check it out.
Engine: cat
1st car: /k/
2nd car: /a/
3rd car: /t/
Secondly, could a picture of the word ride the train? Unless you are using nonsense syllables, I think a visual of the word would be a lovely addition to the app.
Overall, I am very pleased with this app. A few changes would make it spectacular.