Hm...

1. More robust formatting, like being able to hide a portion of your text under a clickable spoiler. We already have most of what reddit had in that regard. but spoiler marking is crucial for any community centered on media discussion.
2. Not reddit, but RES: the ability to click an expando and quick-preview images and videos without loading a separate page, the collapse it back to the compact view once I've seen it.
3. A centralized inbox where I can see people's replies to me, since notifications seem inconsistent.
4. RES: The ability to collapse comment threads so I don't have to scroll past deep-nested conversations that are less broadly interesting.

That's really about it, feature-wise. Otherwise it's just a matter of getting the population here to sustain content generation.

Edit: added #4