There are minor differences between the original and the reprint, but those differences are not enough reason to buy the reprint if you have the original.
There are some sculpt differences (different USSR Battleship, Cruiser, Destroyer, US Fighter, different size Battleship for all powers, different version of the Japanese and the Italian (Japanese in Italian Brown) Artillery, and a different version of the German Cruiser) but in my opinion those sculpt differences are not reason enough to get the reprint if you have the original.
Further, there was a minor change to the board (In the first printing, the territories of Kiangsu and Manchuria had both Chinese and Japanese national symbols printed on the map. In the second printing, those territories only have a Chinese symbol.) and also, Larry and Kreighund attempted to integrate the FAQ from the original into the rule book for the reprint.
If you want to compare the original rule book with the reprint rule book, the pdf of the new rule book is available here: http://avalonhill.wizards.com/rules
I hope that addresses your question.