Pong. Many 2p options exist. 2 1p modes: either play 'first to X' or 'how many points can you get before the CPU attains X'. X is definable.
The main-menu bg is kinda pretty.
The ball's trajectory can't be changed by either your paddle's speed or relative position. So you can't actually do anything to increase the chances of the opponent losing.
When the computer missed, it seemed to be for no good reason rather than because of my own skill. I think that in a 2-player competitive game, having your opponent make a random mistake just validates your own skill and attests to your superiority. And no-one minds that. But in a 1player game, assuming you're playing what is allegedly a game of skill - random mistakes by the computer opponent just make your score feel arbitrary.
Lesson: CPU flaws need to lie in their limitations. Not in random screwups.