Chaotic design. The whole game just looks like a mix of random "cool" ideas, with the story beign recycled from previous two games and changed here and there, so it wouldn't be *exactly* the same. The design process also lacked competent management, with a focused vision of a coherent world, which in turn resulted in lack of consistency in the game overall. Much like Fallout 2, where some places did seem out of place and the atmosphere of settlements was often extremely diffrent (though it managed to keep it close enough).
...