This looks like a darker, more low fantasy Dishonored. I've never played any of the earlier Thief games though, so it might be like rolling your eyes at World of Warcraft player calling Warhammer a rip-off.
If Dishonored wasn't incredibly spiritually similar to the earlier Thief games (aside from the emphasis on offensive abilities), you might be right - but I in this case, it's an apt comparison. A lot of people are comparing this Thief to Dishonored is because Dishonored "did the Thief thing" better than this Thief game appears to. Dishonored was very much about exploring huge, open levels with tons of routs and options and hidden knicknacks. I really worry about how linear this looks - but time will tell.