let's only look at objective facts, and that should be enough to tell you why people are trashing 343i:
Halo Reach launched with more than 10 playlists and dozens of modes, one of which was a completely new one called Invasion, Firefight returned from ODST and was fleshed out like crazy
Halo Reach launched with hundreds of armor customization pieces, all of which could be unlocked by simply playing the game
Halo Reach launched WITH COOP and with a functioning Forge mode
Halo Reach launched with more maps
Halo Reach launched with a fully fledged custom game editor
Halo Reach launched with a detailed career stats tracker that had all your statistics available to see
now lets look at Infinite:
3 playlists with 8 game modes total
no coop at launch (need to wait 6 months)
no forge at launch (need to wait 9 months)
less maps than any Halo launch
customization extremely limited by design and highly monetized while still selling the campaign for 60€
custom game editor is EXTREMELY limited (we are talking worse than Halo 2) and broken
no career stats tracker or anything of the sort
all the people defending Infinite only have 3 arguments:
1: "bUT it'S FReE!!!"
2: "tHEy WiLL eVeNTUALly patCH it!!!"
3: "BuT THe gAMepLAY is GOOd!!!"
and the answers are simple:
1: no it is not! it is 60€/$ with a cut out and bastardised + unfinished MP
2: great! let's develop for 6 years, then delay for 12 months and still release an unfinished product!
3: the gameplay OF EVERY HALO IS GOOD... that is not an excuse for anything they are doing...
and which Halo has the best gameplay is a purely subjective thing. Some say Halo 3 is still king,
some love Reach, some even like the shitty Call of Halo 4 ways... and others liked the Power Rangers in Space Halo 5 gameplay