Sumo

Hungry Sumo has one, entertaining, original mechanic; and that's enough to carry a fast-playing little Flash game, though not enough to build anything bigger around.

Your sumos (pink-belted) and the opposing sumos (blue-belted in early levels) bounce around the window, rebounding off the sides and each other like billiard balls. Each time sumos collide, they both lose size -- the bigger sumo causes more of a loss than the smaller one. A sumo reduced to the smallest size that impacts an enemy switches sides.

As you mouseover a sumo, it eats rice, swelling in size; however, if it impacts an enemy while eating, it "pops," turning into a baby and switching sides. Consequently, you want to mouseover when there's no danger of impact and quickly move away at other times.

Sumotori Dreams is a) a goofy but minor little game that's fun to watch but not precisely fun to play, b) an impressive physics implementation in very tight form, c) an illustration of why the demoscene is still relevant: Take your pick.