I would have gauged the response from critics as positive, so *shrug*. I guess it was, in a sense, "mixed". But I see that as a very good thing for any somewhat niche game; if it appeals to literally everyone it's probably missing something, the fabled "soul".
Levito described it very well in that Isolation is uncompromising in its commitment to stealth, survival horror gameplay. It really embraces the concept of "survival horror" in how it strips the player of any sense of power and places them in tense scenarios where the objective is almost always to escape rather than confront. I do love how committed the entire game is to this idea, right down to the checkpoint save stations requiring you go up and manually "activate" the saving system. The design as a whole, in that respect, is very thorough.
Stylistically and presentation wise it's probably one of the best games of this year. The vision is comprehensive from top to bottom, in play design and menus to simply the flashy graphics and ambient audio. It's instantly immersing and convincing, and even though they were working with a hefty load of reference material I think the art and audio teams deserve a lot of praise.
I did have some issues with obvious Alien AI rubber banding and the way the narrative presents itself, but those will be subjective criticism.
In the end it'll come down to how much patience you have and what kind of survival horror you like. If you enjoy feeling empowered yet overrun, like Resident Evil 4 or past Alien franchise games (EG: Alien Vs Predator), you might feel a bit frustrated. If you don't mind slow burn presentation and play that requires attention and patience I think you'll love it.
It's easily one of my favourite games of the year. I'm just surprised CA and Sega were willing to fund an Alien franchise game committed to the style and vision of the first film over the second, and managed to deliver on the premise with design and production values.
