I'm a big Thief fan as you might guess from my forum name
DS was not too bad considering it was meant for PC and Console and had to make some sacrifices for the different platforms in gameplay, the first two were PC only games but DS did have one of the scariest levels of any RPG game ever during the Cradle level, just awesome played in the dark alone with headphones on.
No beating Thief Gold and Thief 2 game-play though, especially with the graphical mods they have had since release and also the wonderful T2X.
Are you Taffers aware you can download for free and legally The Dark Mod V 2.0 now? No need to install Doom 3 first any-more (it uses its game engine) its pretty much one click and go, it really does play like Thief now, one of the best fan mods in any game ever IMHO, you can download from its interface dozens of good fan missions too, would recommend doing the default one and training one first to get used to the controls and interface, then (small) download through game "A Night to Remember" ... Its very good indeed. Will certainly keep me going until Thief 4 arrives next year with the dozens upon dozens of fan missions to try yet. The Dark Mod
As for T4, I really don't know what to think? Its been delayed a lot, no traditional Garret? graphics look very good but graphics are not everything, looks like stealth is still in though, for sure better than nothing and hopefully its a winner.