We've all been in this situation. You're playing a game, and really enjoying it. As you play, the gameplay gets tougher and tougher, and the storyline comes to a climax, you meet the final boss that the whole game has been leading up to, his graphic is huge and awe inspiring...

And you beat him in a rather easy two minute fight. All the tension is broken, and it leaves something of a bad impression on an otherwise spotless game. The moral? Boss battles count.

One very common mistake that I see in boss design is making the first boss too early. When it's early in the game, you'll make a powerful looking boss, but you won't be able to make it difficult because it's still early and you want to have something to do later on. These bosses are a bit pointless, as they remove the excitement from meeting a powerful looking boss later in the game, and actually finding it to be as strong as it looks. It's probably better to make a mini-boss or something that looks like it is. It is a mistake to pump your bosses full of air.

Another thing that I see sometimes is making the bosses get boring. Someone will design a good system for hurting the boss, and make it hard by increasing the bosses life rather than making the system change as the boss takes more damage. It's usually better to avoid just increasing the speed of those fireballs the boss shoots, or making him have a lot of life. It's far better to have the bosses system change to reflect the damage he has taken, like making a robot boss pop out wheels and try to squash you once you destroy its feet.

Lastly, do your best not to make the boss battles too easy. This can be hard, as putting a system into place to stop the player from dealing damage too quickly is possibly the hardest thing to program in a boss. Always remember that people will admire you for having a hard boss (within reason. No one wants something that kill them in the first three seconds of the fight.) and they will scoff at you if your boss battles are too easy. Remember these things, and your boss battles may be greatly improved.