I don't know if anyone else has posted an opinion on this but I've just watched the film for the first time in a few years and I really enjoyed the whole set up of Johnny's story. They should have kept Matt Long for the entire film in my opinion - his tone and /the/ tone of the first part really worked. As soon as it switches to Nicholas Cage the cheeseballs start flying (not a Cage-hater btw, quite enjoy some of his films).
IMHO, the Matt Long actor would have worked better had the GR story been about Danny Ketch, not Johnny Blaze.
_
Every person that served can be called a veteran, but not every veteran can be called a Marine.
while they probably could have done better than Nicolas Cage, there were some elements of the story that wouldn't have worked as well had the entire story been about a young Johnny Blaze;
-Johnny leaving Roxanne for years
-Johnny and Roxanne both becoming successful
-Johnny attempting to follow the right path in life, not drinking or doing anything bad
-Johnny living the life of solitude
-simply the overall fact that even before Blackheart and Metistopheles show up, the tragic events of JB selling his soul and Barton dying still seem to haunt him every single day.
-Sam Elliots character which is one of the best parts of the film probably wouldn't have worked as well opposite a teenager.