Disclaimer: I also had a lot of fun with this game but I got it for free with a graphics card.

Part of it was getting rid of the old beloved characters. Shaundi, Pierce, etc. were well loved among fans and sorely missed when the game out. People found the new characters boring and generic, but I don't know if that criticism survived past the release stage.

It also released with quite a few game breaking bugs which had to be ironed out. Par for the course with big budget games these days, frankly.

As a fan of SR3 and SR4, I missed the zaniness of those entries, but that wasn't a common feeling among fans of SR2.

A lot of people hated it for how "woke" it apparently was by having... people of color in it? Commentary about racism and feminism or something? I don't know, it's been a while since I played so I can't recall any instances in particular of it being "woke" enough to offend people who care about that. As a woke SJW myself, I felt it was pretty good on that front without being overbearing.