The screenshot you based it on has aspect ratio issues, it's not a 1:1 pixel ratio. Some pixels have been doubled.
So I tried to follow the 8x8 tiles for the gui.
Some things I tried to fix.
1. Margins, I removed the bottom part of the gui box to make more space around the text. I also re-arranged the name tags and the arrows.
2. Stronger font for better readability, I'm not sure it's more readable, but I think it sticks out more. Not entirely sure about this though.
3. Softer appearance with more AA and 4 tone palette for the GUI.
4. The :L5 text field can't really be placed anywhere else, so instead of wasting space I added 'level' for clarification. I think it looks more interesting, but it might just end up cluttering it.
5. I wanted pokeballs that looked more like actual pokeballs. Since I had to stick to the tiles I couldn't add any spacing in between.
The hp bars look a bit like windows progressbars, lol..
I think rounded looks better, but I wanted it to blend in with the GUI arrows.