Birthright was an incredible world with fantastic design, if one does not account for the rules. Please allow me to clarify.
1. Birthright was an incredible world. The world of Birthright was based not so much upon Tolkien and other high fantasy, but upon British myth and faerie tales. The elves were somewhat elemental representations of the ancient wilderness of Cerilia, godless in both the game's reality and in the sense that they could not be civilized by human standards. Dwarves were even more elemental, being partially formed of stone, and instead of the berserker dwarves that were so common in fantasy at the time, they were instead a very ordered, methodical race. The goblins were the monsters of the deep, dark forests, who would kill you as cruelly as possible. The awnsheghlien were the singular monsters of myth, far more powerful than what a human could achieve. Dragons were tied to the life of Cerilia, and were inscrutably beings of tremendous power, beauty, and arrogance who were not to be trifled with. This focus on the myths and faerie tales gave the world itself a deeper mythic resonance than one receives from any other D&D campaign world, the majority of which were based upon high fantasy and swords and sorcery literature which were themselves based in part on ancient myth.
2. Birthright had fantastic design. Realm magic provided powerful spells that required magical energy that ran through the land in streams. There was a workable method of having players play as rulers from the very beginning of the campaign, and the game changed because of that. Races were even more restricted than normal AD&D, in an effort to preserve the cultures introduced within the setting. In fact, for the first time, humans were limited. Without having a bloodline, humans could not be mages, and were instead limited to the flavorful but less powerful magician class. Only Anuireans and Khinasi (humans from Anuire and Khinasi) could be paladins.
3. Birthright was marred by the rules. Seriously, the 2nd edition rules had to be bent left and right to accomodate for the various systems introduced in Birthright. Bloodlines weren't balanced. Domain turns took 3 months each, meaning that a war could take your regent's entire youth. The card battles weren't as streamlined as they should have been. Thanks to the need to have lots of realms for players to pick from, there's not as much negative space; too much of the world is settled and marginally civilized. All these culminated in a brilliant campaign setting that really illustrated that 2e had grown long in the tooth.
All this said, I do believe that 4e is perfect for Birthright, but I believe that it would need to be reworked. I've been working on some ideas myself, and the very first change that I believe would have to be made would be to make every PC blooded. This wouldn't mean that every PC would be a regent (that would be reserved for paragon tier), but being blooded would solve the sticky problems of the default 4e player character's power level and the access to high and realm magic. I have more ideas, but I've probably bored you enough
