The 12 principles of animation number 4#: arcs

an arc is the edge of a section of a circle, if you were to follow the arc it would create a full circle. An example of this in reality is pendulum.
a good example is in kingdom hearts when the protagonist (Sora)  attacks with his keyblade, he uses an arc movement to allow his attack the furthest reach in his field of vision. this also is a good example if anticipation.
bad example: Tetris because when the pieces are being rotated they don't arc they just turn but by not arcing it does not waste time in game play when the pieces are falling down fast. 

The 12 principles of animation number 3#: squash and stretch

squash and stretch is used to give an object a feeling of realism by using gravity upon it, a easy example to understand is when a ball gets squashed when it hits the floor and stretches back to its original form as it heads away from the ground. another example that relates to games is how a character can squash and stretch when jumping, running, walking etc.  

The 12 principles of animation number 2#: anticipation

anticipation is all about getting ready for an action for example when someone is about to kick a ball they lift there foot aim then kick the ball making it move. a good example is when you are about to slash somebody with your weapon in fable 3 as the character throws their arm back in to a position where they gain strength as the player we know whats going to happen next. in games the anticipation has to be instant to when the player presses the button or else it can look instantaneous instead of believable.
on the other hand final fantasy XIII while in exploration mode the jumping animation seems like an exaggerated hop instead of realistic jump due to the lack of anticipation. 
anoth example i recently found was a glitch when climbing in assassin creed 3 the anticipation for the character to climb sometimes upwards sometimes misses a action to make it realistic

the 12 principles of animation: number 1# appeal

the characters have to be appealing to the audience for the audience to take an interest in them; there are several ways to make a character appealing the extremes being really cute like the cats in the kinectimals game for the Xbox 360, to being sardonic or eerie like the little sitters in the Bioshock game.
a screenshot from the kinectimals game
concept art of a little sister from bioshock