thief 4 has some stupid cabinets you can hide in from the guards even if they are chasing you, the guards wont open the cabinets and find you because they can't. Even if you were in plain sight and in the light and about a foot away, just pop into that cabinet and the guards lose instant interest in you. It seems as soon as you enter a cabinet the guards alert state gets turned off. the cabinets are everywhere, just makes stealth pointless.
Plus you are not actually playing Garrett from thief 1, 2, 3.
It's been a while since I've last played Thief 4, but I am pretty sure that isn't correct. I remember guards looking inside the cabinets. Maybe you were playing on a low difficulty (I've only played the highest) or this is something that has gotten patched away later on.
However, I've played the game two or three times, so although I agree that it has its weeaknesses, it can't be that bad after all It received a lot of criticism, but lots of the things criticised can be found among TDM fms either.
I think the main issue with it is that it was designed for a way to big customer size, as for whatever reason everything produced today needs to be AAA. Five years of development and a team of 100+ devs if I am not mistaken made the development surely rather expensive, and the sells simply didn't suffice to render it a financial success. A smaller team, a shorter development cycle and everything aimed at a smaller audience would have probably been the better approach.