It's kind of crazy but Alicia getting replaced by Rose early on in the game is where a lot of the frothing anger is coming from.
I've heard the game also has some technical issues (slowdown, battle camera that wigs out in small spaces and next to walls, for instance), but most of the discussion seems to stem from Alicia and her DLC. Which is disappointing, but not entirely unexpected from this company. I'm still pretty excited for the game, but I'm kinda twiddling my thumbs and hoping they make a version for PS4 with the DLC included as well.
This sounds stupid and discouraging developer doing anything unconventional for party member.
I follow someone on tumblr who was posting about the game, sometimes addressing this and she said there are story-based reasons for Alicia not leaving to tromp all over the world with the other characters, too. She also addressed some concerns with how the party members handle her leaving and apparently some players feel like they dissed Alicia, which is a misunderstanding of what was said. v(0_0)v
I'm not even sure what's so great about Alicia that so many people would be that upset. I dunno, maybe she's an A+ top tier character for the few hours she's in the party.