The ending was disappointing. I'd really been enjoying the Kane versus cops aspect of it, and was perfectly happy with the idea behind the proxy thing.
When they started talking about ultimate power, shady clans and stuff, I felt a bit let down. "Ultimate power" is a really bad concept to use; it's very abstract and not revealing, in that when a character is driven by the persuit of 'ultimate power' it doesn't tell you very much about them (as opposed to a character being driven by a desire to find out who killed their father, or being driven to save the empire, or whatever). It's nebulous, weak, and adolescent. All that 'dawn of time' stuff... it's a copout. I would have been much happier if they'd dropped the whole Indigo Child plot and just had it that the real murderer was trying to make contact with his dead wife or something.
But then, to make things worse, they suddenly decide that they're not happy with the game being occult and that it should be sci-fi instead. Suddenly you're looking at "AIs that gained self-awareness via the net" (oh please) and "chroma." Midichlorians, anyone? That was a really, really bad idea. At least if you don't try explaining things in a scientific way, your plot holes can be covered up by ambiguity and 'mysticism.'
The anime/matrix-esque fights on the rooftop and in the hangar were really stupid too. OK, I get that Kane has increased strength and speed, increased mental fortitute and visions of the future. But the guy can fucking fly and do super charge-up mind wave psychic beam attacks? WTF?
It's a damn shame, because for the most part the game carries itself so maturely. But then they go and ruin it with this puerile "You are the only one who can save the entire human race" crap.
Anyway, enough about the story. The design of the game is also pretty heavily flawed.
Much of the time the things you are allowed to do are non-choices. For example: the scene opens with Carla sat in the chair at her office desk. The only thing the player can do... is make her get up out of the chair. There's a big flashing icon for the action at the top of the screen. Pushing the right analog stick upwards does not require a massive amount of skill. So why make me do it? Why not have it happen as part of the opening cutscene, and hand control over when she's standing up, at a point where I have a real choice of things to do?
For a game which advertises itself as having a dynamic story that adapts to your choices and decisions, it's... well... bullshit. Suffers terribly from "figure out what the designer is thinking" syndrome - when playing as the cops in the first diner scene, if you try leaving before you've found some stuff she'll go "I can't leave yet, I've not found the murder weapon" or what have you which is fair enough, but if you try the same thing in the Laundromat she goes "I think I'd rather look around some more." Really? Would you? How fucking wonderful for you, bitch, but I'm the guy pulling your strings and I've run out of things to interest me here so I want to leave. That's not dynamic story.
In truth, the entire way the dynamic story is implemented doesn't work - all it does is decide which bits of information you get given while moving you along the same rail all the time, meaning that if you choose poorly you'll end up playing the game in the same way as usual but you won't have a clue what's going on. Cracks in the system start to appear when characters refer to bits of information that you never got given (I encountered the "who the hell is Jade?" issue as well).
The action sequences. The action sequences didn't bother me that much - I got very frustrated in a few places where my analog sticks just seemed to fail to register presses (most notably in the sequence where you hide in Tiffany's apartment), and with the controlling your fear / balance beam stuff there was no obvious connection between the buttons I pressed and the way the pointer moved (figured them in the end by finding a sequence of presses that seemed to keep it balanced). The rapid-tap stuff was tiring on my fingers but generally not problematic (though a few places where you have to pump it all the way up were irritating - my fingers just don't move that fast after playing for four hours).
Though talking of the simon-says sequences - and this is something I noticed in God of War as well - I find myself concentrating too much on watching the lights to pay attention to the actual action scene as it happens behind them. I'm not sure how that can be dealt with. Making the cues nonvisual might work - you hear a sound, you hit a direction - but your attention will still be divided across what is going on onscreen and the buttons you should be hitting. The things it asks you to hit kinda correspond to the action (i.e. yoink both triggers right, he dives right) but not well enough that you could figure it out without the prompts. So you do need cues of some kind... if they could be married together with the action such that you can easily focus on both at the same time it might work better. Maybe something as simple as moving the prompt icons to match the character's on-screen position would work, so that you can watch both at the same time.