games I like have a shot,or shots that are not easy to make but very satisfying when you make them.
the thing that makes you want to play just 1 more game.
it can also be a mode or combo.
something that you did a game or 2 ago and you almost did it on your last game.
one of my favorite tough shots was on pinbot. the target at the far right just above the right slingshot.
when lit it advances the planets. I would sometimes take the glass off and just practice that shot until I could make it every time. another fun shot that when you can make it is on whirlwind.
making the right ramp shot to lock the ball from the right flipper. it is a very tough shot but if you time it just right you can do it. pat lawlor once said a good pinball game is easy to learn, easy to play, and hard to beat. I guess that's what I like.its hard to explain, but you just know when a game plays right and feels good. taxi is another one for that. getting all the fares and getting the jackpot. it can be done but its not easy.

Mof, you should really design a game.
The way you analize a game is amazing. I think you could bring pinball to a whole new level.