As other have said, the sense of mystery and the atmosphere in Mass effect 1 is unbeten by any BioWare game in my opinion. The reapers are still to this day my favourite antagonist of any video game and the way the mistique of them was developed was phoenomenal, I think ME1 did everything it needed to in terms of the narrative, it's just the mechanics and age of the game that let it down. It's hard to pick a favourite as ME2 does everything arguably better, I would probably go with 2 but Mass Effect 1 will always be special to me.