Thief 1 & 2 are two of my top favourite games, so I'm in the "bargain bin" camp as far as T4 and NuGarrett go. The negative feedback that I've been seeing from the current Thief communities (TTLG, TDM, etc.) isn't very encouraging. I don't think this game is going to do the Thief franchise much good given the split that Thief:TDS caused, which is a shame.
I think that a modern, AAA quality Thief game, based more on the first two games rather than Dishonored and other recent "stealth" games, would have been amazing and would have been successful without needing to implement dumbed-down mechanics. Thankfully, the Thief modding community is still fairly strong and active with a plethora of additional content for the original games and new(ish) projects like TDM and NewDark.