1. Great plot that make sense with a lot of real decision options. Less beaten to death tropes, no Mary Sues, goody two shoes, and stupid evil for the sake of evil characters. The character motivation should be logical and believable. 2. Polished fun gameplay that involves as much of my very long list of suggestions (sent to Larian) as possible.
That's pretty much it. I don't care too much about zealous D&D 5e implementation, number of party members, or if some classes will be left out.