In CoS 2, there were a pair of Christian crosses in the crypt. I remember commenting on them to myself at the time, but not making a big fuss over it, and I didn't even include it in the final review.

I am now kicking myself over that.

CoS 3 is about stealing the holy grail.
No, not "a" holy grail, or the hammerite equivilent. We are talking about the holy grail.
It's also clear this is Garrett we are playing with. So lorewise, this mission is about as non-canonical as you can get. Without giving away too much, the grail isn't at the local chapel, it's actually with a local noble, so this is actually a mansion robbery, with streets.

Lets start with the streets:
They are spectacularly designed. I love how close to the original game they look.
The mansion is less nice, but once again, it matches the original games look. However there isn't much variation in there, most rooms look the same.

Within that mansion however, every floor is marble. Carpets are present to jump between, and this isn't as bad as it first sounds: the mansion is small, and plenty of moss arrows are present in the store at the start (Justifying my impulse to mass buy them). So while I don't like the mansion, it's not really flawed.
Then we have the streets... there are room brushing issues out here, the AI seem hyper-alert. I genuinely wondered if it was a situation where the map had one huge room brush, but it turned out that was not the case. There is also an issue that all the city watch guards slowly form together into one large patrol. Amusing, but probably not intended.
Put simply, AI are very buggy in this mission.

The story is actually OK, though the issue with using a real religion, is that it the stakes of the story become linked to the players views and experiences of that real religion, and unfortunately, this unexpected addition of a real religion isn't used to tell any story that can't already be told if it was the "chalice of hammers". It also makes the claim that pagan's are the same as Satanists... something which isn't so unlikely in the context of T1 (Remember, this is before T2 came out and made the pagans more friendly) but it's also completely untrue in the case of the real world, and is quite unpleasant in it's implications.

All in all, this mission plays decently, looks great, but I do wish it's AI performed better. It feels like the mission is generally high quality, but just needed a bit more testing before release. I also find the story progression a mixed bag.

In sad news for me personally, this is the final circle of strain mission. The last part of a very strong early Thief FM series. It's a shame it's final entry was a bit weak, but CoS 1 and 2 were two of the strongest 1999 FMs out there.