That thing could be more entertaining with little additional weight on the preloader if:
The liquid was enclosed in a container of a more complex shape. Something with convex inner edges, nooks and crannies.
The whole container rotated around the center of the flash window based on the position of the mouse pointer (say, for instance, that the direction from the center of the window to the mouse pointer defines ‘down’, and rotate the container appropriately.)
On topic: EBF3 has a minigame in the preloader. So do other games, I recall seeing one very recently, but the actual game escapes me.