Part of the game development process is game balance. The Quality Assurance phase, which looks for bugs, problems and compatibility issues, is your final chance to balance the game. Well, except for patches, but we developers hate patches as much as anyone and would prefer to have a balanced game right out of the box.
Game balance is important, at least as important as stability, ease of use, graphics and audio.
What some people may find balanced is not balanced for others. Of all the game design pieces, game balance is one of the harder ones to get right. It also complicates things when you have both a single-player and a multiplayer mode. What may be balanced for one mode may not be balanced for the other. The perfect game balance takes the player to the edge of failure every single time, but the player almost always succeeds.