Stealth meter: You might argue that people in the shadows see better so shy not just raise the gamma a little when you're hiding? Some blue tint at the sides of the screen is just stupid. It was done in other games but games with fewer stealth sections. The light gem was better for simplicity's sake.
Design: Let's face it. The first two games had so little graphics that most of it was left to our imagination. But it was clearly a medieval steam-punk and unique to the series, fondly remembered and respected. Thief 3 was the first game with actual graphics and detail and while it was a bit more confusing as a setting (mainly Medieval sprinkled with Victorian steampunk), it bloody worked. This one? Bah... I'm seeing a few nice things (lots of cracked wood, medieval alleyways), but that brothel with bunny ears is a bad joke, as are the late early 1900's civilian clothing and those 1800's german helmet guys. They went for a more Victorian setting (meaning Victorian/Edwardian steampunk, sprinkled with too little Medieval background), but they forgot that steampunk belonged to that era so you end up loosing that dark futuristic look. What you end up with is a gritty Dishonored setting, not a progressive Thief design. I don't particularly like it. I do like the detail tho... But it needs interactivity. Remember how interactive the game seems just because of the shadows and extinguishable lights and noisy floors? That's all you had, but everything seemed to have an effect.
Story: no news yet, but coupled with AI, this is what's gonna sell the game. I was a huge fan of Thief 3's dark story and just mentioning the words "Shalebridge Cradle" brings shivers down my spine. I want to see them top that. Otherwise, I don't really care, be there Hammerites, Keepers or whatever.
AI: just make them take a break once in a while and search more randomly. Make them look over their bloody shoulders from time to time. Make them believable humans, not robots with a programmed path. There is not one stealth game which does this... be the first if you want to be worthy of the Thief name. Just go to a museum, talk to the guards, see how they behave based on what they expect to see. True stealth is judged by how difficult it is to adapt.
I'm not expecting to like the game. At least not as much as I liked the old ones. I hated Deus Ex HR and even made a thread a while ago displaying my concerns over Eidos' take on Thief (which had just been announced then), but was laughed at or called a paranoid. And trust me when I say that this is one time I pray to be wrong.