This is where I tell you that I love Halo and I’ve been around since the beginning so it legitimizes my point and or argument. But I think what’s more important is the observation of the game and community that I can share.
I have always been quite advocated and opinionated on the Halo forums and game forums in general. I feel that the community of games these days hold a big part of the games balancing and general change.
When I would be on the forums over at Bungee as Spartan 307, I seen a lot of threads about wanting things changed in the game; but none as dramatic as in Halo 4. Not even Reach.
Halo 2
In Halo 2 the biggest thing was the Pistol and the BR. People were mad that it was out of the game and replaced. There was a lot of complaints about bxr, bxb, double and quad shooting glitches. Lot of glitches in Halo 2’s time. Can’t remember a lot that people really wanted changed
Halo 3
Obviously one of the new things that people were getting bent about was equipment in Halo 3 as it was the biggest change to the game. The bubble shield caused a lot of cat-n-mouse tactics with Sticks, Shotgun, and Beat-Downs which people didn’t like. The Regenerator was probably the biggest issue with the game as it could turn a un-fair shift in power instantly in a skilled shoot-out.
People -Yoinked!- about the change in the BR going to a hit-scan weapon and the spread. Hornet was OP but then later rebalanced. One last thing worth noting was the first TU brought a much needed fix to melee.
(Side note: does anyone remember how in Halo 2 melee’s were probably at there best? A standard hit would bring you down to quarter shields while a jumping melee on someone would take down their shields. Man I miss that)
Halo: Reach
Most of us still remember the days of Reach and how dramatically different it was in terms of Halo 3. AA’s was Bungie’s evolution of Equipment which was horribly imbalanced, especially Armor Lock. The DMR and Armor Lock were constantly being brought up to be balanced or removed. Vehicles were highly under-powered from Halo 3 as well which the diminished their overall usefulness. And the Banshee Bomb 
So now we have Halo 4. Which we all know what the most talked about things are:
Over-powered DMR
Descoping being replaced with Flinch
Custom Load-Outs
Random and unfair Personal Ordinance Drops
Sprint being made a player trait
Weapons removed from map
Loss of past Playlists
Removal of Forge World
Removing of Campaign Theater
Removal of Custom Game options
The list can go on and is highly subjective, but this is the meat of many threads on these forums. Obviously there has been such a dramatic shift in Halo since this game. Halo Reach still played heavily on the fundamentals. While it introduced Load-Outs and Armor Abilities, it still offered classic gameplay elements.
I wanted to share how thoughts and insight on how the game has changed. I find it interesting however how as this game further evolves and changes, the less and less people play it. Which goes against the old saying that change is good.