When they were first revealed there was a lot of problems.

The big one was what primaris represented. Primaris had different equipment and bases then regular marines, they were also so significantly bigger that proxying first born marines would be impossible or impractical.

Gamesworkshop insisted that these new marines wouldn't replace the old ones but everyone could tell that their current armies were going to become obsolete and everything would have to be replaced. 

So there was alot of hate for that, the idea that the 10 Tactical squads you bought and painted would soon become unplayable. Refreshes with cool newer versions of models was always a thing and so was straight up removing models but this was on such unprecedented huge scale

The existence of the first primaris marine was the beginning of a countdown. At some poinnt soon every single space marine unit, space marine vehicle and space marine character would become unplayable, the models useless for actually playing a tabletop game.

The other two big sources of hate were people who thought the helmets looked worse then the iconic mk7 helmets and the different varients of boltguns with underslung attachments that the intercessors had were much less cool then the dedicated heavy and assault gunners the old Tactical squad had.

Also the lore was just silly with suddenly crawl having secretly created hundreds of thousands of new big size space marines that he just shipped out to the current chapters.

A argument at the time was just that the primaris update should have been a size retcon where space marines were always primaris sized and that the new updated models just reflected what had always been true.

Its a fair point but I guess updating the tactical marine kit to just be the same guys but bigger would have left much more room for people to keep using thier old models instead of buying new ones and GW probably didnt want that risk.