That it was such a success and led to an incredibly successful franchise despite that, shows the power of its writing and strong characters and world-building.
A similar thing goes for another legendary series: Assassin's Creed. The first game is borderline unplayable, but it was still enough of a success to spawn AC2 which was a masterpiece of storytelling, although the fundamental mechanics weren't really smooth yet even at that point, and improvements were made all the way through brotherhood to AC3 and then black flag.
Over time, the story-telling and characters weakened, although there were some gems along the way such as odyssey.