Recently entered into the Blender Game Contest was a beautifully made game entitled 'Megagolf' by Supersocks on BA. This is a true example of what can be achieved currently with the BGE, both with graphics and gameplay.
The game is based on Golf, but with a more futuristic approach as the courses take place in 3 dimensions (see the pictures below). The graphics are crystal clear, using the new GLSL materials in the BGE. Players without GLSL supported graphics cards can also still play the game.
Supersocks explains the gameplay:
Use your mouse to aim and rotate view. If you have wheel in your mouse you can zoom in and out with it.
Hold down left mouse button then move your mouse up or down to adjust the putt strength and left or right for direction. Release the button to launch the ball.
There's two kind of surfaces: Standard in which ball bounces off when hit and magnetic which ball can attach to. Also there exist speed pads with arrows which give you extra speed in that direction and jump pads which launch the ball upwards relative to the surface.
Have fun! ...and don't mind few badly implemented courses.
There's a thread with more information and comments here. (plus alternate download links)
*Updated to version 1.03*Â Download the game (20mb) from this link
And something else worth looking atÂ is the trailer on Youtube. Watch it here.