Hated it first time I played it now it's up there with my all time favourites and I've put more hours into 6 than into 5 and 4 combined. I think it's a bit like Marmite in that few people are indifferent to it.
That said, given my early skepticism I do think that some reviewers didn't give it long enough before writing it off but it doesn't help that the prelude section is not a good introduction to the game. --- 'What did you say?! Insects' life doesn't compare to human lives!'