I want to like this game but so far I'm struggling to.
Stat points: For a game that seems to want to promote stealth as an option, why have this stat being the most expensive? Immediately you're making an already difficult path, even more difficult. When there seem to be plenty of other methods provided to change the difficulty level this seems a very odd decision.
Menus: No consistency in menu controls, entering menus often feels clunky but it's very easy to accidentally leave them. An example of inconsistency would be the PDA, you use tab to open it but once you've moved off the home screen you can't easily close it again, you basically have to reverse what you did to get back to the home page and then press tab. At times the mouse wheel works as intended to scroll text, other times it does nothing and often it doesn't scroll what you want it to (eg the email screen, scroll wheel, scrolls through the emails, not the text of the emails). It just doesn't feel like menus were designed with mouse and keyboard in mind.
Gadgets\Abilities: The gadget tutorial was an eye opener. Again bizarre control mechanism that doesn't work on a PC. I actually ended up beating the guards into unconsciousness in the final challenge as I was too confused by the preceding section to be able to do it in the correct manner. I'm assuming abilities use an equally arcane method but I've got as far as working out how to use mine. This is something that should be immediately obvious and intuitive to do.
Mini-games: Whoever designed these should be fired. Even if you removed them entirely and made unlocking/hacking etc completely random it would be better. Not only is the hacking game headache inducing but it's also again abysmal to control with mouse and keyboard. The keyboard controlled word moves far too slowly and the mouse controlled one doesn't match up to where the cursor is pointing (which can make it almost impossible to place correctly).
In summary, this game is badly let down by an inexcusably bad UI and atrocious mini-games. I think a lot of the poor reviews the game is getting would go up to something acceptable if not very good if those 2 things were fixed and it seems amazing they weren't noticed in early testing.