16-Bit is the most important (Score 1)

16-bit Support: I probably don't need to say too much here. Photoshop works in a 16-bit space. Although, just between you and me, I've found this less interestin since I have adjustment layers. I don't have to do a lot of re-fiddling with images in a destructive sense. But that's a personal preference thing.

In my opinion, 16Bit is by far the most important, since the cameras normaly capture 12-14bit/channel and that gives you a gread headroom for recovering highlights and shadows or pimping your contrast, without degrading the final picture. A great raw-import would be nice, also, but there seem to be some (I heared not too great) raw-importers.
But without this feature a professional picture processing is unthinkable, or, at least, mediocre -- which makes me think about the author (the author is a photographer who also teaches image editing).