A new version is always an improvement; it has extra frames of animation and tweaked controls, but is probably not different enough to make it an essential purchase. 2 player games so far have tended to be turgid midfield battles with few shots and neither side retaining possession well, but that could just be down to tactics.
It's a big game for patchers; I've updated mine about 5 times so far, and it's gone from being completely unintelligible japanese, to full english translation including commentary in the space of about two weeks.
I've upgraded with every version of it since ISS Deluxe on the PS1. Some think the FIFA series is better but they're so incredibly wrong it's not funny. I've wasted thousands of hours and probably permanently damaged my thumb on it.