I love Halo 3's campaign. I'm not sure if I would call it "the best", though. ODST included. >_>
Hell, I'm not sure if I'd call any Halo's campaign "the best". But I sure have tons and tons of memories of it. Frustrations, friends, and achievements galore. Halo 3 provided so much with it's campaign, especially being four-player co-op.
I don't think it hits the highs of Halo 1/2 as much, but it's still great. The Covenant is one of the best levels in the series and it was great to FINALLY kill 343 Guilty Spark. The levels that are good I will replay until the end of time, and Cortana I will avoid as much as The Library as it is my own personal hell. The Vidmaster Annual achievement is still one of the best and worst things to do in the campaign and I had to do it
twice. The skull and terminal hunting were great.
Story-wise, it was dull up until the end of Voi into Floodgate, which blew my mind that the Flood reached Earth and spread across Africa. Great stuff, even if the game really didn't make you feel the urgency, it was pretty big. It dies down again when you hit Cortana up until the (bad) boss fight with 343 Guilty Spark. Although, I'd argue that even Floodgate got mind-numbing midway through as you're just going across Voi again. Another issue is that after developing the Arbiter, he gets shafted a bit. I can understand why, but with Halsey, he's still one of the best characters in the entire franchise. Marty's music was great, too, even if it is "Halo Remastered" I loved it, along with the new themes like Cortana's when you find her.
I see a lot of ODST comments and that's fine, I can understand why. I see even Reach and get why, too. Both of them have great gameplay for each level even if the story connecting it are extremely weak. ODST beats Reach easily in this regard if ONLY for having more likeable main characters. But even then, for both, the last two missions are the only ones that have any real weight in the universe and end up being them most interesting parts in the story. My reasons for not putting either one up is that for 1) ODST isn't particularly memorable. None of the enemy encounters are all that great and feel like shooting wave after wave. The open-world streets level is fantastic, but GOD is it dry. There's really nothing much to do in it beyond soaking up the incredible details of the world. The glyphs in the Engineer (yes Engineers, fuck that Huragok/EU/Species name crap, there's a reason why we just call them grunts, jackals etc. It's easier damn it) hidden spots are fascinating and I'm not sure if the meaning for those were ever found or if they have any. And finding Sadie's story was cool, too, but beyond that there's no reason to go back again. Having health again and the awesome silenced pistol was cool, but I never had great use with the Silenced SMG as the only thing I ever used it for was for drones and it was horrible if you're trying to be stealthy.
Reach I love as an overall package, and I always go back to play the campaign, but most of the issues are there. Poor story, most encounters aren't all that memorable (at least it doesn't suffer as much from wave after wave) and as amazing as it is to see Reach fall, the important stuff isn't hit until The Package. Bits of the game I would highlight are glitching through Nightfall, vehicular battles in Tip of the Spear, almost all of Long Night of Solace up until the gravity is turned back on, Exodus amongst civilians, New Alexandria's freedom of flight and Club Ererra, and Lone Wolf. The Pillar of Autumn is a personal favorite of mine, though.
Halo 2's campaign I felt was amazing, I loved seeing more of the Covenant through the schism and the Arbiter's eyes. Great character with a real arc in that game. The introduction of secondary characters was cool, too. The Prophets, Tartarus, Half-Jaw, Hood, Keyes, more Johnson and Spark (kinda. I hate that guy). The first couple Arbiter levels aren't all that I agree, minus the Heretic leader boss fight and the Banshee section. Quarantine Zone is scary, but Sacred Icon is epic. Gravemind was a highlight, Upsrising's dull, and the beginning of The Great Journey is, too. My issue with Halo 2's campaign is how it ends. I don't think we need to know more about that.
Halo CE is the one I'd probably put closest to "the top" or "the best" only because it nailed that sense of wonder and mystery. Seriously, the start is amazing, then you land on a giant hula-hoop and discovery after discovery with fun gameplay to boot. Being stealthy with the sniper rifle is a joy and an award unto itself, and I mean beyond the beginning of Truth and Reconciliation. The Library and Keyes aren't my personal highlight and if you asked me years ago I'd say the same for 343 Guilty Spark. But I've come to appreciate the level a lot more recently because of the constant state of dread. That feeling of foreboding is throughout the level, and I've come to like it. You're a big supersolider and now I'm scared of some freakish, disfigured, alien spore-zombies? Great stuff. The Maw is a personal favorite of mine, too. I love that level so much from start to finish.
And I think I've said enough about Halo 4 before. I've enjoyed all Halo campaigns, and to that extend, the series (even Wars) in its entirety. But Halo 3 should be remembered for being amazing and having The Covenant be one of the best levels in the series for both story and gameplay. Up there with The Silent Cartographer and Assault on the Control Room for me.
I swear though, these games are the best in co-op. That's part of the reason why they've lasted so long for me because I can always count on having a good time or bonding through them. Any of them. Halo 3 is the epitome of amazing co-op fun, and Halo 1-2 co-op is how my friends and I used to chill with each other.
You know this thread and Halo 3's anniversary just make me thankful that this series exists. Without it I wouldn't be into this hobby nor would i have the friends I have to this day. Plus, it's pretty much the best game series ever.
Of all time.