My son LOVES trains, and he also loved the Curious George movie. He has several of the books based on the Rey's style, and the PS2 Curious George game.
Curious George Takes a Train is the first George book I've bought "sight unseen" (from Amazon.com). However, since my son loves both trains and George, I felt it was a great fit.
Granted, my son seems to like the book. Out of the four books illustrated/written in the Rey tradition, my son owns three by Martha Weston. The other--Curious George Goes to a Chocolate Factory--is illustrated by Vipah Interactive.
Weston is heavy on the black charcoal as it is (as seen in the shadowing of books like Curious George Visits a Toy Store), but she is *especially* heavy with the black illustrations in Curious George Takes a Train. In fact, it often looks as if a child has taken a black crayon and (no lie) colored vertical streaks of black right on top of the people!
It's very unattractive, in my opinion, but kids don't seem to notice these types of things. I also felt that the story was a bit harrowing for a George tale (a little boy runs from his father after a toy train, the gate closes behind him, and the boy almost goes out in front of the tracks--but George saves his life.)
The story is a bit quick...it goes from the Man with the Yellow Hat strolling off with Mrs. Needleman in the station to George climbing up and messing with the numbers and letters on the train schedule--and then off to saving the boy!
If your child is a train enthusiast who likes George, he/she will likely enjoy this book. However, as far as stories go--and illustrations--there are better books in this series, in my opinion.