There are many different reasons games are enjoyable. Graphics, gameplay, challenge, depth, complexity and theme are all important aspects. Some games lack many of these elements yet benefit greatly from competition. The mano a mano ass-kicking floats many games because it's just plain fun to kill your buddy or destroy him in a simulated sport. Of course, the competition itself would not be any fun without effective gameplay, and that's what Slap Shot does well.
Let's not kid ourselves, Slap Shot is just a suped-up version of pong. It's one-on-one hockey in super fast style. The graphics are weak and cheesy, the story, set-up and backgrounds are silly and weak, but it all doesn't matter when you start playing against your opponent and you start laughing your ass off with the high-octane fun.
You use the joystick and two buttons (MAME info says 3 buttons, but I can't figure out anything button 3 does). One button hits the puck normally, the other gives you the ability to curve it by moving the joystick after you make contact. Your "goal" (pun intended) is to score a goal on your opponent. Each game goes until a preset number is scored by the winner or time elapses.
Like most Vs. fighting games, you play two out of three games to determine the winner of the match. Also, like Vs. fighting games, if you are playing the computer, you play successively more difficult opponents if you keep winning.
But make no mistake, while the game is fun against the computer, the game is built for two humans to go after each other with each goal/volley only lasting a few seconds. High intensity fun for all.
There are a few other features, for instance you have a power bar, and when it fills up you can execute a special shot by pressing both buttons simultaneously. Also, your goal starts with shield/blocks in it to repel the first shots and then the blocks disappear when hit by the puck (breakout style) leaving your goal exposed.
The venue changes between matches and some of the rinks are shaped differently, changing some of the angles. But in the end, the game stays very simple, very fast, and very fun. And in fact is one of the most fun 2-player "versus" games I play with my friends (yes I have some friends). As such, I will be inducting into the Hall of Fame for 2 player Versus games.