I'd love to improve Feralheart a little. As it is, it's one of those games that seems to be stuck in alpha.
I'd start by optimizing things. A game so simple and with such meager graphics should NOT be lagging out on a high-end PC.
After that, I would take a look at adding in simple functionalities - the ability to rebind expressions to keybindings, to turn off that bloody click to move, for example. Tidy up the UI, small steps.
After that I'd take a look into bigger things - adding features. I'd add some wildlife for players to interact with and hunt, an item system, combat and stats. Pvp would be optional - much like in WoW, you could flag yourself. Items would give either a tiny boost or no boost at all. The aim would be to keep the sandbox aspect where you don't HAVE to do anything other than sit around and chat/RP, but giving you options for other things too.
Maps would be overhauled to add things of interest, wildlife and other fun stuff. Glitches with terrain would be fixed, and sizes/shapes would be different. In addition, I'd incorporate some of the most popular maps into the game, holding a poll every now and again to see what one to add next.
The addons system would be improved. I would try to intergrate a UI where you could add and remove mods you had downloaded at the click of a button, while also compiling an archive online to track them all. If you party with someone and they are using a mod you are not, you will be notified (this can be turned off.)
Finally, graphics. I'd overhaul the textures, add new and more varied ones, and remodel everything from the ground up. Feline model doesn't need too much tweaking, but Canine does. I'd also introduce Deer, Horse and Lizard models, while deepening the amount of customization you could do to any of them.
Different colored markings, more than one marking, recolorable paw-pads, teeth, gums and tongue. Every aspect of the body could be individually resized, and some like tails and ears could be duplicated.
Overall I would have some LOFTY ideas for the game that would take me forever. And I'm kind of stopped by the fact I'm not the world's best coder. But, I would try my ahrdest to deliver on all therse fronts, even if it meant slaving away restlessly for years.1