Birthright could have been a contender.
By many measures, the ambitious second edition AD&D setting, should have been.
It was a technically well-done product line for sure. The interior art was tasteful and evocative. The maps were attractively drawn and plentiful. The game accessories such as army cards and battle maps were nicely done. (Well ok, the cover art was horrible and cheesy.)
It didn't lack for product support either. Well-executed supplements detailed nearly every culture on the continent from the bog-standard Anuireans to the lizard-riding dastardly Vos (Russians). They also added new rules, accessory toys, and mini-games like naval combat and trading. It had it's own computer strategy game and six novels as tie-ins.
And most importantly it expanded D&D tabletop gameplay in ways that DMs and players had lusted about since the 1970s. Domain management was not shifted off to a hazy semi-retirement “end game”, it became the central assumed arena of play. Players started not as the rootless and down-on-the-heels schlubs we all know and love, but the genetically-endowed rulers of realms--or the heads of temples or guilds. Whole new rules subsystems were worked out for running your realm and fighting wars (complete with a simple and easy, card-driven wargame.)
Looking back, Birthright had the potential of taking off from where the less-known worldgames of Hyboria, Midgard, and Magira ended. So again what went wrong? Why didn't this game go onwards and upwards? And did anybody really play this for long?
Was it TSR's setting bloat of that period? Was it that the game play was too different from the experience of the standard party-based campaign of that time? Too abstract in its domain management rules? The creepy eugenics-sounding bloodlines business? The evil empire corporate machinations of WOTC? Or what?