In an interview with Crunchyroll, Thief's narrative director Stephen Gallagher has commented on why Eidos returned to the franchise.
Asked why the studio decided to bring back Garrett for a reboot Gallagher said:
"Well, I can't really speak on behalf of the minds at the company, but we were looking back at the original games, and naturally, there was a lot of love for those first few games. They were something very different at the time–people saw this first-person game and everybody asked 'Where's the guns?'
"You had Deus Ex with this awesome, branching narrative, and Eidos basically just went 'Really? You guys didn't know this shit existed?' and it was a chance to fall in love with this universe all over again."
While Garrett is most well known for stealth it seems the developers are intendo on allowing players to go about a heist however they see fit.
He says that in the game "your life is the single most precious thing you have" which is why the thief warns against killing but that doesn't mean you can't murder when the occassion demands it or even indiscriminately.
Later in the interview it senior producer Stephane Roy said that if you choose to be completely stealthy and leave no trace it will be tough – even on the easiest difficulty.
While the last Thief game, Deathly Shadows, allowed players to switch between first and third person mode Thief is entirely in first person and Roy explained the decision saying:
"We feel that to make sure the immersion is just perfect–with headphones, with next-gen, the graphics, the sound–after playing for a few minutes, we wanted to make sure that you are Garrett. When you see your hands picking up objects, or you pickpocket someone, when you're that close to the guards, we want you to feel that tension. The first-person perspective feels natural when you are this character, this is your body. It's also very affecting from a narrative perspective."
Thief is set for release on February 25th, 2014 in North America and February 28th in Europe on PC, PS3, PS4, Xbox 360, and Xbox One.