An extremely subtle thing, but one that stands out simply because such a simple element of RPG game design - interacting with the characters around you - had never been pulled off quite so well. Sure there were multiple options on what to say in the likes of Oblivion or Baldurs Gate, but nothing that really showed you peoples' emotions through their facial expressions, or let you get really up close and personal with the many corners of the galaxy. The conversation wheel in Mass Effect was so enjoyable to pick apart that simply wandering up to everyone and discovering their backstory was a gameplay element in itself - something that when hulking bat-faced brutes like Wrex provided amble talking points, made you feel like you'd made a genuine connection, creating a landmark moment that would influence everything else thereafter.
