Before even reaching the first enemy in the game I noticed these this:
• Missing music on the intro logos.
• Max resolution of 1600x1200, so playing on a larger resolution monitor the game will look small on screen.
• Textures use a low quality upscale filter that can't be disabled (especially visible on text/logos).
• No motion blur like the original had, so the wobbly water distortion effect looks straight up broken.
• Missing fade in of the main menu with the cool music ramping up.
• Keybinds are completely broken by default, the key to move downwards is not even bound by default.
• Music is using WAV versions of the original MOD tracker music. The WAVs have a ton of white noise in them.
I really wish more care was taken with this before it was put on GOG.
It looks like there's a separate Direct X launcher for the game to run it at a higher resolution and add anisotropic filtering if that means anything