I'm most excited for the different races having different combat and fighting abilities.
For instance, I think the cats should be able to claw by default; Their usual attacks causing bleeding and more damage than the regular little punches. Less knockback, but more scratch. Like having a knife at all times. I also think cats should be able to climb to make up for their lack of jump; After all, I'm sure I'm not the only one here with a cat that has gotten stuck up a 50 ft tree.
I think Rats should be able to take a bit more of a beating and roll around more for better escapes, and most of all be good at hiding... Perhaps pickpocketing?
But yeah, the main features I want are climbing to make up for the weaker jumps, as well as new combat to balance them out. I'm excited the way things are going with this game, though!