Well, besides FR/LG being two generations ahead of Blue and featuring capabilities such as GCN connectivity as well as connectivity with RSE, as well as the introduction of new Pokemon, places and opponents, including a stronger Elite Four and Rival, I can't say there's much a difference.
I'd get a DS, though, and buy Diamond or Pearl when it comes out April 22. It features a slight bit of a backwards compatibility with FRLG/RSE, as well as letting you fight trainers all over the nation/world.
But if you have $25 to spare, go ahead and pick up FR or LG.