So I played the first few levels of the Filcher demo. I still think it's an impressive effort for a single developer, but it's just really really rough.
Great sound and lighting are what made the first two Thief games and The Dark Mod what they are. The ability to tell where guards by the volume and position of their footsteps is so fundamental you don't really realise what you're missing until you have to do without. With no effective sound portaling, it sounded like all the guards in the level were tapdancing around me all the time and I had no idea where they were.
Jumping can be janky too. You know how in TDM when there's a bit of a downwards lip on something you're trying to jump off, sometimes jumping just doesn't work? Like a horizontal metal pipe you haven't surrounded with a block of nodraw_metal. Dial that annoyance up to 11 for Filcher.
On the plus side, the level design itself is fine. I like the idea of giving an overall stealth score based on both loot and ghostyness. You get a score out of 50 for the amount of loot you get, so if you get 80% of the loot you get 40 points. Then you get bonus points for not blackjacking anyone, not getting spotted, setting off no alarms, and so forth. It's a neat little system. And I do kind of like the almost art-deco style.
A little bit of polishing up would make this a hell of a lot better. It's just not quite there yet. The thing is, you could make the same levels and gameplay in TDM in half the time and it would look and sound twice as good.