it received hate because reach is a more professional take on the halo series, alot of people played it before playing the other titles and didnt understand it, and some expected halo 3, not to mention there was alot in the alphas and betas that never made it to the final, such as space pvp battles, and ai map creation on forge, alotta the weapons are also under powered compared to halo3 and 4, you have to work harder on acuracy and straff movements, and the physics are more advanced in the way of realism that bungie had been trying to implement, i think bungie could have added more to it, and should of kept their dlc list for those of us who bought it all, considering the online count isnt exaclty reliable in the way that it doesn't add people alotta times to the poll count, not to mention the dlc play list was taken off when everyone finally bought it, you cant expect people to by it if your not gonna let them use it in matchmaking(not many want to wait for people who have it to randomly pop up, i have all the dlc and havent played one of em ever, so that's ridiculous)......
certain weapons such as the plasma repeater and needle rifle should have had more shield piercing capabilities, while certain shrapnel weapons such as the DMR should have had more effect on armor, they also could have done updates that added more weapons into the game so the fans would keep interest and would have maybe inspired 343 to do the same, some story additions would have been amazing to, after all i would like reach to have more levels, would have been neat to play as other reach survivors like buck from ODST, not to mention chief was on reach, could have played him there, or playing as jun who left with halsey, could have also added forge dlc, the plasma pistol also ran outta charge power to quickly, the brute shot (seeing that it shoots giant metal heated spikes) should have done more damage, and been involved on more maps, its to bad they didn't add the brute shot, has always been my favorite halo weapon of all time...
the needler should have had more melee damage as youre stabbing others with a spiked bladed gun, the difference in mind between a blunt weapon and a bladed weapon on your opponent, additions to forge could have involved more fx and gadgets, maybe vehicle additions like the revenant or hornet, let you spawn up props like pelicans(unusable because they had issues with them being used) or some animals that run around, maybe change the skybox as an option, could have added skins and textures, or even different items to the building sets, maybe new decor, a custom color editor, let you color the vehicles, or even design your buildings with art and pics, more vegetation or natural items would have been nice, more custom gameype capabilities and spawning methods, along with custom objectives, many things they could have added, but they were always to focused on the pvp sadly