The first game takes my vote over ODST. The fist was great for a game in general, while ODST was great for a Halo game. ODST was very near to the feeling of constant looking over your shoulder and having minimal support as did Halo CE.
CE however, had a less complicated plot, and gameplay felt like you had a reasonable chance on Legendary. Useful weapons were more common because every weapon was useful and fun to use. Some of the changes, for instance the plasma rifle, got me irritated at Halo 3's campaign, but applied to a less powerful unit with less armor and resiliance, a plasma bolt that travels nearly as fast as a bullet, is a hindrance, not a gameplay balance. And now I'm going off on specified tangents, so I'm going back to my original point of story.
In Halo CE, you were on a ring world, in a place you didn't want to be, with people who didn't want you to be there, or to exist. You also had a plethora of weapons. Hmmmm. Now, with your support all but cut off, no idea of what was going on, and intelligent enemies, it was an uphill battle. But, due to perseverance, respawning, and a fairly decent supply of weapons, you could do it. On Halo 3, anyone can do it on any difficulty. And the story was a half-assed attempt to tie up loose ends while still leaving room for a sequel, what I mean is, the good guys won in a triumphant and inspiring victory but the heroic main character is nowhere to be seen. The attempt to bring all of the 'rightous and just' characters together felt contrived and obnoxious as did the gameplay. Don't get me wrong, it's still fun to co-op it and the multiplayer is great. But story wise, I'd rather listen to a monkey on a piano than Cortana, which brings me to my next point.
Shut up Cortana! Yes, yes I could watch you die. Now please unfreeze my screen, I'm being shot at here and the only reason I'm playing this campaign again is to practice whatever skill I'm lacking at in multiplayer.
The tentacle thing was most irritating as well, I wanted to kill the flood/zombie/idiot right then and there. But no, you see, we had to rescue our digital damsel in distress, Cortana, from her perilous plight of plethoras of pain. But, she's not even real. She is a series of ones and zeros. So, I ask myself, why do I care. Simply put, I care because I'm an achievment whore and wanted all of the achievments. But, story-wise, I don't. And why should I? She offered nothing useful except in the first game. But then again, the first game wasn't a Halo game so much as it was a work of brilliance on a Halo disc.
The point being that the story and gameplay go hand in hand in the first game, kind of like two hands or something of that nature. The frantic, adrenaline charged, apprehensive mood that the first game induced was incredible. ODST, almost, so close to being that, stands out more for it's failures than succeses. But it's failures were all minor things, I.E. weapon idiocy, all encounter's being remarkably similair, blah blah. It's story however, was good. Not great, but good. It went well with the gameplay. All it needed was a silenced Battle Rifle.
Good Lord this was a long post.