Yeah, the PAL version had the same music as the Japanese version, it was only the American one where they changed it (something about paying royalties to artists whoose songs were sampled, I think). As I say, I think both soundtracks are excellent; unfortunately Sega's never made a version that allows you to freely swap between them. Instead, any re-releases of the game have just used the American one.
I love the ridiculously inspirational lyrics in the JP/PAL opening
. Probably the only 16-bit game to encourage you to keep an open mind and believe in yourself!
But yeah, the time travel aspect does wonders for the game's replayability. It's insane how much detail ended up going into the game as a result of that mechanic. The loading times when time warping are a bit annoying though!