Games are interactive. When you play a game, you have absolute control of the character and the camera. You are the person driving the story forward and making the moves. Therefore, the animation not only has to look good but has to be so from every possible angle.
For example, if the player rotates the camera around in a third-person game, they will see the walk or run cycle from a new angle. This angle can reveal things such as knee pops which may not be visible in the normal camera view. These are things a game animator needs to take into consideration to ensure their animation holds up whatever the player might throw at it.
Animation in Movies
In the case of animation in movies, the animator is only responsible only for animating whatever is in the field of view of the shot camera. In other words, they just need to worry about one camera angle at a time. While watching an animated movie, the Play button is hit, and the movie plays. There is no way you can rotate the camera around to look at the whole set. Therefore, your field of vision is stuck at whatever the camera is viewing.
This allows animators working on a movie to cheat in certain ways, as they know that the shot will be seen from only one angle. Therefore, if it looks great from that particular angle, that is all that matters. However, this does not mean that film animation is easy. It simply means that the difficulties associated with game animation are different from those faced in the film animation industry.
Creating Game Animation
The game animator will be exposed to several more types of animations than typically found in a movie, such as what Pixar or DreamWorks produces. There might be animations being made for fantasy creatures, combat manoeuvres, giants, scripted events, etc. There are many different types of cycles associated with a game as well, not just walk and run cycles. For example, most games will have a breathing cycle, crouching and walking cycle, an idle stance cycle where the character is standing still, walking forward aiming a gun, lying down and crawling, crouching and shooting, etc.
There are a lot of games which are driven by body mechanics, so it is essential for the game developers to spend a lot of time perfecting the body mechanics to be successful in games. This is not to say there will not be any acting scenes in the movie, but if you go back and revisit the last video game you played, you will probably notice just how dependent games are on body mechanics.