I’m working my way as a top UI Designer. I would love to hear all of your opinions on my UI!
Not much a UI artist myself, however -
My Opinion / Suggestion
I enjoy the color scheme! Perhaps the sword icon can be moved off the edge towards the right a bit.
One great tool you can use are ViewportFrames. These are like a normal Frame, except you can showcase models / parts from within them. This saves you from having to create separate images for what you’re trying to showcase, and honesty all around look quite good!
If you’re interested, here’s a link you might like 
Viewport Frames
I think it is looking nice! Especially the shadows in the letters, how did you do that?
I would recommend moving the exit button to the top right corner, because that is what most users are conditioned to seeing. Along with UI, comes UX (user experience), which strives to ease the experience of users when using user interfaces. Try to implement practices that most people would automatically understand or be used to already. I would also add padding around the sword image.