Was it your first Thief?
To be clear, I don't think Thi4f was bad in absolute value. It even improved on some core aspects of Thief: for instance the custom difficulty settings for self-imposed challenges (eg ghost) were great, and showed some of the devs at least were paying attention to the community.
However, the loss of charm in the setting thanks to the confusing pseudo reboot (no Pagans, no Hammers, no Keepers, replaced by a more generic and forgettable big Bad -- which I don't even remember), greater linearity of the levels, forced escape sequences, no true rope arrow, ... greatly limited the creativity you could bring to bear during the game... which was the whole point.
I also intensely dislike the monochromatic art direction. The engine was great, but was given scant opportunity to render pretty things (more of a personal taste thing; some people like the "100% gritty backstreets all the time" style. I'd have proffered to rob opulent banks with marble and shiny bronze security systems rather than wallow in lovingly-rendered gutters, but that's just me. ).
Still, what's left was actionnable if you could take it for what it was. The mutilated zombie of a great game concept can be a good game on its own terms. I'd just have preferred an unmutilated, live version, and many fans felt the same; it looks like the franchise is dead for good because of that, and that's a crying shame. :-(