If you have played through the Thief series a few times, and want an extra challenge, try playing by these self-imposed rules:

- Expert difficulty
- Obtain all loot
- Pick all pockets
- Take no damage
- Deal no damage (except as strictly required by a mission objective).

Note that blackjacking someone does cause damage, so the only way you can incapacitate someone is by using gas, which, as you know, is only available late in the game and is very scarce.

As you can imagine, the "take/deal no damage" rules really make obtaining all the loot quite difficult in areas, especially in guarded rooms with locked chests. But before you say, "impossible!", I have completed both Thief 1 and 2 following these rules. Thief 3 wasn't out back when I did this, and I am still waiting for it to go on sale on GoG before trying it.

Anyhow, give it a try! It really adds an extra level of challenge and freshness to this series of awesome games.

Is there any way to tell when you've obtained all the loot during a mission? I've played missions before and thought I had all the loot only to discover I missed one or two pieces at the end. But it seemed that the only way to tell is to finish the mission and look at the final stat. Any way to determine it during the mission itself (without consulting a walkthrough)?

You can always see how much loot you currently have by cycling through your inventory. To see the total amount of loot available for a mission, save your game, commit suicide, check the stats page, and reload.

This is similar to "ghosting" through Thief, where the added challenge is to complete a level without leaving any traces or making your presence known. That means not allowing yourself to be detected (the guards must not catch even the faintest glimpse or sound from you), no killing/incapacitating enemies, and not leaving anything behind that might hint at your presence (rope arrows, moss puddles).

Personally, I wouldn't play by those rules. Thieving on the hardest setting is challenging enough for me, and I never play games to the point when they become too frustrating.

Isn't ghosting technically impossible on certain missions? Anyway, I've often considered doing a playthrough kind of like the one the OP mentioned, as it would provide some extra challenge (I've already finished all three games on the hardest difficulty settings). Then again, my usual playstyle involves lots of reloading when I'm spotted, etc., and this would just make me reload even more. I think the next time I play I might try to avoid reloading as much as possible and actually try to deal with the consequences of getting detected when it happens. Actually use things like flashbombs for escapes and stuff. That would be a big change in playstyle for me and sounds like it could be fun.

You will get a lot of practice doing this if you play by the above rules. The only way to get to some loot is to let the guards see you, lead them on a merry chase, lose them, then circle around back to grab the loot before they do. And yes, it is a lot of fun. :)