Not sure if this has already been covered but I would really love to see the old character information implemented again. Being able to check what % of kills a party member has made, strongest enemy killed etc seems like a small thing but it was a really cool feature. I'd even like to see this expanded on somewhat if possible. Maybe have a big codex of monsters that gave you a description of each with a nice bit of artwork that got unlocked when you killed it.
You could even incorporate this so that the more creatures you kill of that type the more information is unlocked. By the time you've killed 50 odd skeletons you've pretty much summed up that smashing them with a blunt object is the best way to go.