Text should be easy to read no matter what resolution or dialog you're reading (tooltips, menus, item descriptions etc). I liked the font and colors of Fallout 1 & 2. They were very easy on the eyes. NWN is the complete opposite, very blurry text and hard on the eyes even if you play at low resolutions.
Also make sure that conversations are MODAL. NWN handled this very badly by allowing actions to interupt while in the middle of conversations. Also make sure time is paused during conversatsions. Don't want my buffs to run out just because I'm taking my time when talking to someone.
The UI of DA1 was clean and ok but lacked a lot of things like good textual feedback during combats. Don't hide to-hit rolls and such to the user. Preferably include an option like Fallout had for Combat Messages, where you could set it to verbose mode.