Halo: Reach is a game made by Bungie Studios and was the prequel to Halo: Combat Evolved. It was supposed to be the greatest Halo title, but turned out to be terrible. It broke its own canon many times and introduced many new features that were terrible.
They broke the original Halo gameplay so badly that the golden triangle (guns, grenades, melee) turned into a square made out of moldy turds (Armor abilities, guns, grenade spam, sprint melee).
They removed many features that made what Halo was and removed dual wielding, and the most iconic weapon of Halo: The SMG. The Battle Rifle was also removed and replaced with a new, more overpowered weapon.
Bungie also brought back the health system which made sense, but made grenades way more powerful, without changing them.
The game was overall terrible and only ran for a few weeks off of hype. The game couldn't even hold #1 game on Xbox LIVE for more than a few weeks. Every other Halo game accomplished this for years, and even when they were not #1, they were still pretty high up.
There is a conspiracy where Bungie intentionally made Halo: Reach a bad game because they didn't want the fans to miss them and so 343 Industries
could have an easy time winning over the fanbase and selling Halo games by turning Reach into something playable and remaking the first Halo game without changing a thing.