KeeperFX can be played in any resolution. Originally it came with the 320x200 resolution, later the 640x400 resolution was added. On modern PC's 1280x1024 is standard for people with 3:4 monitors, 1366×768 is the most used resolution overall because of laptops, and 1920 × 1080 is features on many a gaming-pc.
KeeperFX supports the higher resolutions, but unfortunately the game features sprites for just the two original resolutions (e.g. very small). As people still want to be able to see the icons, buttons, creatures, etc they are automatically made larger by the game (nearest neighbor). This makes the game look really 'blocky', 'pixely' or 'ugly' depending on the technical term you prefer.
I know what you're thinking: We should all kill ourselves because we can't hope to live with this in the year 2015. I say, yes this is a good idea, but I have a better one: Make bigger sprites.
It is possible to download the KeeperFX GFX source data here. Is there a sprite-artist here who is capable of making (a few) higher resolution sprites? When in a game of Pictionary I get the task of drawing an 'egg' people guess things like 'a six' and 'a rock' and perhaps 'a rock with a circle around it and loads of arrows', but never 'an egg' so I'm not it.
I could do automatic resizing though:
Original Sprite:
Resized by KeeperFX:
Resized by image editor:
Who can do better?