So, what boss is the most important to games in general? A strange sort of question, perhaps, but I'd like to think that each particular boss role has its own place and quality that's important to a game's flow, and to the player's enjoyment and interest.
So what kind of boss is the most important?
Is it the prologue boss?
Maybe he hasn't got such an important role... maybe he doesn't even exist. The prologue boss can often set the mood for the game or for boss fights in general. He can be there to teach the player how to play, or might simply be a hook (something big and flashy that makes the player go "whoa", but ultimately unsubstantial). On the other hand, is such a boss even necessary?
Is it the first boss?
The culmination of the player's first trials through the game, the first boss is often an easy sort of test, to make sure the player knows what he's doing, and to provide closure on the first leg of the game and direction for the beginning of the story (if there is one). Easy or hard, you can't dispute that a first boss is pretty important. And let's face it, even if the game's only got ONE boss, it's got a first boss.
Is it the second boss?
I'd like to think that the second boss holds more importance than people give him credit for. To me, the second boss can often be more of a hook than the prologue boss. It's the time when you trust the player enough to give him a challenging experience, one that'll catch him off-guard, shake up his nerves a bit and hopefully give him something to remember.
Is it a middlin' boss?
Different games go at different lengths, and oftentimes most of the game's bosses will lie somewhere between the two extremes. Obviously, each boss here has to not only hold his own as a level boss, but find some way to be memorable. The worst kind of boss is the one you forget immediately after fighting. But then, maybe one of these bosses will hold the story's big twist...?
Is it a recurring boss?
You know the type. The ultrosian pest who pops up just when you don't need him and gives you trouble. Far from a requirement (and maybe not even a full boss), this guy gets merit for his tenacity. And if he's well-done, you're SURE to remember him. But still... is he of any importance?
Is it the penultimate boss?
This is the boss that occurs right before the last boss. Sometimes he's the fast-paced challenge to balance out the siege that is the last boss. Sometimes he's meant to be a phony last boss that you're supposed to fall for. More and more nowadays, several bosses are cramming themselves into this "penultimate" position. I guess it's supposed to be more dramatic if the challenge lasts longer, but I think that too many of 'em, one after another, can end up cheapening the significance.
Is it the final boss?
The big BANG! at the end? The climax of the game? None can refute the importance of such a position, but maybe it's that irrefutability, that'll put another boss above him, in terms of importance. I mean, ya GOTTA have a last boss. Leave him out and the game will feel... incomplete. He's important, but he's... expected. And, again, if the other bosses don't hold their sway, the players might lose interest before even MAKING it to this guy.
So, bosses' roles in a nutshell. But who ends up holding the importance? Is it the guiding battle that teaches the player? Is it that pivotal fight where the player is hooked? Is it the final clash at the end?
Go forth and cast thy vote.