If you just take the text of both games and use that as a comparison, the various dialogues of both games I would say while Fallout has more complexity in resolving tasks, the quality of writing and how the decisions can effect the game is about equal. Just on pure text, Fallout would edge out Mass Efect to a degree but that is just a part of the overall experience of both games. Again, when it comes to games, it is the fun factor that matters most. The level of the overall entertainment value of Mass Effect is higher than Fallout 1.
This is merely just my opinion, but Nick, it is defintely a game to play. Rent it and give it a try.
EDIT: Pidesco, if the game isn't fun then there is no point in playing it. It is the only way I grade a game. You may grade differently, but to each their own.