Either you obviously didn't knew Halo 2's storyline or you just couldn't understand the concept of the storyline. Remember, the campaign missions were all quallity made, nothing was quantity but the amount of enemies they sent in. Coming from a reality check, the Ark is a real place but doesn't have any forerunner technology on it and Bungie tries to pull off by comparing reality to Halo 3. Don't play Normal and Easy difficulties, play Heroic if you happen to play a lot of FPS and Legendary if you have that many patience in survival.
I've played Halo 1 and Halo 2's campaigns numerous times over. I've read all the books. I know every piece of the story that has transpired before Halo 3. The game does not make sense. They were not quality made, and the "quantity" you speak of is a lie. Bungie claimed the Battles were bigger than ever, this is simply not true. They are the same size as they always were. I played through on Heroic and beat it in 7 hours, first try.
The multiplayer, you might as well play Forge and change the way you play. There are man cannons to speed up travel, obviously. The "Equipments" is what changed Halo 2's core gameplay in Halo 3. Go and make your own game varient and add speed, gravity, specific weapons, vehicles and respawn points to your satisfaction.
All of this is fine but... (read the next point)
Hell, go edit the weapon's rounds and damage to your liking.
You can't edit weapon damage or clip size.
If you still think Halo 3 sucks, tell that to millions of players that plays it. It's frankly impossible to have them change their mind.
The game just came out. I think you'll need to give it a little more time before fans start reacting to the campaign. And most people who play the game still think Halo 1 and Halo 2 make absolutely no sense, even though virtually everything about the game is explained by Cortana as you walk around.
The multiplayer is growing on me. Some of the maps are just fucking terrible, they're all out in the open and there are no pre-placed weapons so everyone just gets Assault Rifle kills. I realize I can change this, and intend to do so.
My main complaint is the terrifyingly awful single player. It is not "overhyped", it is significantly worse than everything that came before.
None.