Alright, but not amazing, doesn't really warrant the hype.
I downloaded it last night and played through the first chapter and a bit... Is it good? Well, yes, it's sort of fun - the water physics are nice, the way debris gets washed throughthe corridors. If you allow yourself to get immersed in the game you CAN feel the claustrophobia of tunnels filling with water and the desperation of finding a place to come up for air... But that probably requires some imagination - and is probably helped by playing late with the lights off and a can of beer... Similarly to Valve's 'Left4Dead' - the experience is probably enhanced by the environment in which you play and the time of day you pick up the pad.
It reminds me at times of Prince of Persia, Forgotten Sands - some of the platform elements have a certain 'parkour' feel to them - but not to the extreme of 'Mirrors Edge'. The cover shooting is okay - it won't win any awards though. So far the story and characters have been so-so, not distracting, but not completely engaging. That said it's fun to play, I am finding the environment can be a bit 'samey' at times - making exploring a little uninteresting and making it difficult to orientate yourself. Kate's equipment is pretty neat though - the Mavi is fun to use, and the map works well.
So what gives? Well, it's fun, it's a nice little game. It's not that expensive at 1200 points, but it's largely about showcasing the water physics engine it seems... I would say if you like a platformy explore/cover shooter and you are interestied in the physics engine - then go for it. If you like a platformy explore/cover shooter and you are NOT interestied in the physics engine, then wait until it's down to 800. Hydrophobia is good, it's interesting to play - but it's not really amazing.