Okay, a possible flamewar starter here, those who just want to insult fans of different games please don't answer, also, people who hate halo as a rule and do not see a difference between games keep it to yourself, it's just a question I'd like answered about a standpoint that conflicts with everything I see. But if you browse the internet, you'll find hate aimed at Halo 2 on everywhere from TVTropes to bungie's own statements. However, I'm fairly well traveled, and among people I've met personally, Halo 2 tends to get the most praise of the series.

I'd like an answer as to why. This is the standpoint I seem to see on a personal level:

High Points:
(NOTE: Due to the hatred of ODST which I outright attribute to FanDumb, I KNOW why it's hated, I disagree, personal opinion, however, it will not be discussed here. Please.)
Halo: the Flood, rebalancing the shooter.
Halo 2: The story, character development, rebalancing yet again, introduction of internet.
Halo 3: Revision and perfection of internet, introduction of builtin community modding tools, breaking the copy-paste level design of the prior games.
Reach: Perfection of the modding tools, best cinematic(not story, but camera usage, visuals, and explosiveness) approach in single player of the series.

So I decided to go through the games and figure out why this is. I have a more specific list of high points and low points of all the games. Having not finished the Campaign on Reach, the points there will be vague and hearsay, I'm sorry, if someone else could flesh that heading out I'd be grateful.

Halo"
Singleplayer:
Story highpoints:
343 Guilty Spark: When the Flood show up.
Two Betrayals: It's alot harder to see a betrayal coming in a story when the character doing it doesn't realize you didn't know what he was working for the entire time. He wasn't trying to betray you, he honestly thought you knew the formula.
Keyes: I'm not sure if this is a highpoint, because you saw it coming a mile away, but it was dramatic nonetheless.
The Maw: Destroying the weapon and annihilating your friends and path home is easily a tense dramatic moment in shooter history, more when you think about it afterward than the actual ingame.

Gameplay highpoints:
Pillar of Autumn: THE level that introduced you to a new concept in gaming. And surprisingly intense compared to later levels.
Halo: You see the ring go up, and up, and up... also the last real variety in the game for the most part.
Silent Cartographer: The midgame breather from CutnPaste tendancy. And the best scenery porn in the game, arguably, as you aren't stuck in a natural bowl the entire time for gameplay reasons.
The Maw: A return to the most detailed level in the game, and even that is massively overhauled. And the most intense battle in the game, followed by the greatest warthog ride in the series.

Low Points:
Keyes: Again, because you saw it coming a mile away.
Cut and Paste architecture, culminating in
The Library: Seven identical corridors with identical battles. Doesn't stop them from being far too massive.

Highest point: The Maw

Multiplayer:
High:
The rebalance of gaming, again. And the inclusion of secrets in mp maps, in a trend to forget those.
Low: Some cutnpaste again, Derelict (OW), and no online.

Halo 2:
Singleplayer:
Story highpoints:
The entire Arbiter storyline(The Heretic, Oracle, Sacred Icon, Quarantine Zone, Gravemind (Arbiter viewpoint), Uprising, The Great Journey): Extremely deep character development on the new protagonist. Portrayed very well mechanically. You may have seen the story a million times, but it was very deep here. Especially as it didn't portray him being a double agent or giving leeway till the very end, where the option was forced down his bisected throat. It timed the emotional climax perfectly here. Possibly the foremost reason I'm even asking the question in the first place instead of agreeing with the mainstream.
Gravemind(shared): It may be a giant cutscene, but it breathes life into the Flood once more after their somewhat stale appearance so far. And challenges both Chief And the Arbiter. This is the beginning of Chief's emotional journey this time around. And the introduction of the coolest villain in the series, a magnificent bastard worthy of Tycho or Durandal.
Gravemind/High Charity(Chief viewpoint): Chief and Cortana's romance is fleshed out up to "Don't make a girl a promise, if you know you can't keep it...", the most tearjerking line in the series so far. And this time you didn't see the separation coming until the characters do.
Gameplay highpoints:
Chiro Station: Okay, finished the game on heroic. Let's try it on legendary! (Nope. Sorry. Died, reload checkpoint.) Legendary is on a whole 'nother level than Halo 1, and is the hardest legendary in the series. And this level takes the cake for the turrets in the habitation area. No cheating AI, either, like the Jackal snipers later on. This is honest difficulty. It is the only legendary level in the original trilogy I haven't finished. So hard it's funny.
Most Other Levelsurprisingly, if they didn't avert cutnpaste, they at least managed to make the battles play out differently each time in this game. They almost completely avoided long boring segments this time throughout the game with the exception of
Low Points:
There were a few segments of boring though, the second halves of Delta Halo, The Oracle and Sacred Icon come to mind where the dev team started to fail in variety. But the quality overall of the gameplay was still improved over Halo 1.
With one glaring exception: The end of the Scarab fight. Thank you kindly, Bungie, for building us up progressively over the course of two very good levels that probably serve as another gameplay highpoint in the whole series as they manage to completely avert cutnpaste and build the tension for... a curbstomp battle against your harassing Scarab. In defense, it's the most believable way the military would take it down, but it wasn't very fun, I wanted a boss battle. It looked better than the ones in 3, but they fought better by far.
Highest point:
Gravemind
Multiplayer:
High:
The most creative maps in the original trilogy, and the successful integration of internet, without sacrificing the satisfaction of seeing your brother's face as you stabbed him from behind. The fact that the only cutnpaste level that wasn't a remake of a halo 1 map being Containment, itself a beautiful dose of scenery porn.
Low:
So far, no real bad points here. More customization would have been nice, but at this point there was nothing disappointing. Everything about it's multiplayer was better than 1. In an effort to say something bad about it I'll say they should have included all the maps in the map pack if not in release, I like Hang 'em High. If I can't download it later, I'm pissed.

Halo 3:
Singleplayer:
Story highpoints:
There were several very moving points, and the brutes were integrated very well. I'll cite
The Covenant, Cortana, and Halo in particular, as they closed off the loose ends of the storyline. Cortana was also heartwarming after the ending of 2. Halo because you finally get to pwn that jerkass 343 with a Spartan Laser. Who had his best lines in the series.
Gravemind and Cortana's characters in particular throughout the entire game had the best lines easily.
Gameplay highpoints:
Tsavo Highway: Long, fierce, and desolately beautiful.
Cortana: An amazing transformation to High Charity. I do wish the Flood had stayed green, however, as this game had far too much brown in it already.
Halo: The callback warthog chase.
The whole campaign succeeded in averting copypaste, but...
Low Points:
It sapped the believability of some of the levels, Crow's Nest comes to mind. An example of going overboard on abstraction in a realistic level design theme. There's no way any installation is built that haphazardly.
The dialogue for every character besides Gravemind and Cortana. It went from deep storytelling to action movie. "More brutes" "Worse."
That line and Crow's Nest were such glaring failures on the final product that I died a bit inside. Also, you think Johnson would have put a bit more effort into something awesome to say as he died. "Send me out with a bang", indeed? From the man who brought you "Two sticks and a rock! For the whole platoon! And we had to share the rock!"? I don't care if you're dying, I wanted an epic rant.
Highest point: Either Cortana or Halo. Both good, I'm leaning towards Cortana for the Gravemind/Cortana banter. But the brown change hurt that level, too. I'm just not sure if it hurt anywhere near as much as the shoddy end dialogue for a beloved character in Halo.
Multiplayer:
High: The mechanics. Customization. It may have taken until CoD4 for the style to catch on, but it started in 3, and now everyone uses it. Also, forge was a great blow for consoles over pc in the war. I'm a PC gamer, and the forge won my heart a little bit.
Low:
The stock maps fell into the same hell as Crow's Nest for the most part this time. Rat Trap comes to mind. Valhalla was also like a slap in the face to the Blood Gulch community, though admittedly it was well meant, just overdone.

Reach:
Singleplayer:
Story highpoints:
Unlike Halo 3, you didn't slaughter character development this time, which is good. Also, the portrayal of the war in the first level, as far as I ever got around to playing, was quite good. People have told me the death scenes were friggan epic.
Gameplay highpoints:
The enemies were much more believable AI wise, and the score system was cool.
Low Points:
From what I've heard, again, there was disappointment over the lack of real character development and how they went out of their way for over-the-top epicness rather that good storytelling.
Highest point: Lone Wolf
Multiplayer:
High:
Had the system created in 3. While the online had minimal improvements at launch, it's hard to go up from the top. Forge's revisions, however, caused a major increase in replay value in Multiplayer. This gave Reach the best multiplayer in console gaming, arguably. Also they fixed the over-abstraction from 3.
Low:
From what I've heard from longtime fans, 343 mismanaged the multiplayer badly. While the maps continued to get better, the servers became glitchridden, and each patch, again hearsay, seemed to create more bugs than it fixed. I know at one point about six months from launch I got kicked from my own Forge game, which we were hosting, because someone accidentally TK'd a connected player while manipulating a piece of scenery. This was annoying. Jetpacks are NOT a low point, cuz from what I've seen, you people who fail to get good results aren't using them right! They're a speed booster, not a elevator!


That's my review, my apologies about failure of research on Reach, I'd like that corrected, and I still would like to have said question answered. Is Halo 2 therefore massively underrated by the mainstream? I'm curious why my favorite installment takes so much hate.

Please help!
And no flamewars or ODST discussion, please. Everyone can keep their own opinion on that particular controversy.