So, usually the beginning of a game is a great time to establish the gameplay and style of the game. And what better way to establish a great game than to give it a great first boss?
Once again, it's all games I've played, only one per series, and all my opinion (which is supreme anyway, so you're guaranteeing eternal damnation if you disagree).
#10: Dracula (Castlevania: Symphony of the Night)
Since Symphony of the Night is a sequel to Rondo of Blood, it only makes sense that there would be an introductory backstory. What's cool about SotN is that it lets you play it, which is basically just the fight with Dracula. However, it's a pretty fun fight, and literally impossible to lose. Plus, it's the only time you can control Richter without beating the game, which is cool.
#9: King Hippo (Punch-Out!!)
The first few fights of this game were really easy, but King Hippo is where things started getting serious. He's the Minor Circuit champion, so you know he's gonna be less of a pushover than the previous guys. And he is, with more powerful punches, much higher defense, and needing to hit his stomach to be able to defeat him. Of course, he only needs to be knocked down once, so... yeah...
#8: Metal Sonic (Sonic Generations)
For being one of Classic Sonic's only bosses in this game, Metal Sonic is pretty cool. He's constantly charging at you, and as you damage him, throws shit at you and starts creating energy fields to get you with! It's always satisfying seeing Sonic punt him into the sky at the end of the fight.
#7: Twilight Thorn (Kingdom Hearts II)
Yeah, of course the best Kingdom Hearts game has the best first boss in the series. Twilight Thorn is pretty creative with it's attacks: weird acrobatic stretches, summoning thorns (LOL), and an awesome QTE sequence. This is one boss I won't forget any time soon.
#6: Kakashi (Naruto Shippuden: Ultimate Ninja Storm 2)
This is where the bosses start getting really good. So, like the other boss fights, it starts like a normal fight. Then, in the quicktime events, Naruto beats on Kakashi with some Shadow Clones, and Sakura fucking destroys the arena. At that point, Kakashi starts summoning Water Dragons to attack you and electrifying the water around you. In the end, Naruto engulfs Kakashi in a massive Rasengan, and you win. Pretty badass stuff, considering the show it's based on...
#5: Diekuu Ohrowchee Revived w/Laambo (The Wonderful 101)
With a game like The Wonderful 101, you know the bosses are gonna be epic. Ohrowchee is the one most people remember from the trailers, and it's a good'un. First, you start by chasing after it in the Virgin Victory for a shoot-em-up section. Once you're done with that, you go on the beast's back and fight it's heads (and Laambo at one point). You get to slam one head into the wall of a passing building, and once you damage that head enough, it turns it's tongue into a sword. You cut it's tongue out and stab it until it dies, then you take control of that head and make it rip off the other one! After this, you jump from platform to platform while tossing explosive barrels at Ohrowchee. Then, you get into a short duel with Laambo, and fire an arrow that pierces him, grab his sword, and slice him and Ohrowchee in half! After this, you know the rest of the bosses will be at least as awesome!
#4: Wyzen (Asura's Wrath)
Obviously, this boss is when you know for sure that Asura's Wrath is going to be an amazing experience. You start out with a rail shooter segment, running toward Wyzen as he attacks you. Then you have to jump up the rocks to punch him in the face. A few QuickTime Events and four extra arms later, and you're shooting at an airship, occasionally flinging it's own missiles back at it. Then you have another rail shooting segment, shooting at Wyzen again and flinging missiles back at him. After this, it's all one big QTE, which consists of Asura punching Wyzen into space, Wyzen growing so huge that his finger is the size of a country, and trying to squish Asura with said finger. But Asura's so manly that he punches the finger so rapidly and so hard that his arms disintegrate and Wyzen fucking explodes! Holy shit, all of my yes!
#3: Colossus of Rhodes (God of War II)
Obviously, after the badassness of the original God of War, we expected big stuff from GoW2. Well, it throws you right into pure awesomeness with the Colossus, who throws shit at you, chases you throughout the city, and has some awesome quicktime events. An awesome beginning in another awesome game.
#2: Ghirahim (Legend of Zelda: Skyward Sword)
Ghirahim really shows the capabilities of this game, and why you should strategize your attacks. If you attack too soon, or from the direction he's pointing, he catches your sword, and may steal it, then throw it at you! Eventually, he starts teleporting around and summons a sword and some projectile-things to attack you with. A good start, for the rest of the bosses.
#1: Metal Gear RAY (Metal Gear Rising: Revengeance)
Metal Gear Rising is the kind of game that cares primarily about being as badass as possible. The opening really showcases this with Metal Gear RAY. It constantly fires missiles at you, tries to stomp on you (which you can parry to slice up it's armor and guns), and fires plasma beams at you. At the end of the first part, you slice up it's blade, then at the end of the second part, you jump across it's missiles, slice through it's other blade, run down a building, and slice it in half lengthwise! I don't know how this fight could be any more awesome.
Well, those are my Top 10 first bosses. Now to be bored until Injustice comes out.
HBM, signing out.