For one this game isn't having just rave reviews, Gameinformer gave it a 7, Playstation magazine also gave it a similar score (Can't remember the exact score, so I might be wrong).
But truthfully, I think it's getting good reviews because it's something new, original and is pretty well executed. I haven't beat it yet, so my opinion is able to change in the next few hours of gameplay, but what I've played so far has interesting mechanics and a very good story.
I do have complaints, the game is stupid hard, especially the boss battles, but it does leave you feeling very satisfied after succeeding. Some of the cutscenes, specifically in the beginning, run to long. The story being good helps, but sometimes its nice to actually play the game.
I do have more nitpicky complaints, but I'll say this: If you want something new and interesting to play, get Cathrine.