Ok, as I see the project is unfinished, but it doesn't mean it is bad.
The current problems, of course, are graphics and the UI.
But I want you to make battle rate chance higher. I was wandering for about 1 minute before my first fight. I am not sure if you should use default random functions, it could be a pseudo-random function which makes the appearance rate higher each time you didn't find a monster. Or something like that.
Here goes the next problem: I can't understand what is happening. You should add some info when you are using some items (net, for example). Like "you can't catch it", "you failed" and etc. You should definitely add some feeling of turn-based combat. Through the sounds or graphics, it doesn't matter.
You should rework map and movement. Add diagonal movement or make a character not to stop when pressing two buttons but continue to go.
I am really happy with your serious approach and different surveys, so I think that you want this game to be better, so I am telling you the truth.
Ok, now here is some very **long term** goals and ideas for you.
It's a reversed Pokemon game as you mentioned. Add some towns and quests. It will make all wandering meaningful. Add some real good element-based damage system, with all types of weaknesses and power. Do some game design research and find out what will make your game so special and which mechanics could attract the possible gamer.
I hope you will improve your game quality and hope we will see you in the next Jam.