Frustrating freezes anyone? Maybe not as everyone seems to be finishing it o.k.
Dunno if it'd help, but have you posted your system specs anywhere? I've got a fairly powerful set-up and I got some sudden frame-rate drops but it doesn't sound like that's your problem. (S'hide uses a lot of moving-shadow lighting, which I love but can be a real frame-rate killer IIRC.)
Anyway, just wanted to say I've finally completed the mission (on easy) and - WOW. The moment when the final challenge kicked off was one of the most jaw-dropping moments I've had in any - well, I was going to say FM but I think I could say any Thief mission, period - and I found I needed some pretty Thief-y skills to get round. More than made up for the earlier frustration, although after exploring one avenue fruitlessly, I did use a spoiler to find out where to go - it was hard enough to get around knowing where I was going, let alone stumbling around cluelessly.
After some consideration, I voted 'Excellent' for gameplay, which may be over-flattering given my earlier outburst, but the frustrations really were outweighed by the good stuff (I'd say I had similar frustration levels with Heart of Lone Salvation, which I also loved despite the difficulties).
Voted 'Excellent' for appearance - the only thing that stopped me voting 'near perfect' was that the fog effects especially got a bit too much at times (especially in crouch mode, which is my default position a lot of the time). Voted 'Good' for story - really liked the whole background ambience of the place gradually being consumed by pagan evil, but at the same time it didn't feel like I could much about it except get out before the whole place went down
Maybe we should have a collection of spoilers for key-hunt-haters so they can do all the legwork as quickly as possible and then enjoy the final section. It really is quite amazing. I know S'hide says he's never going to make another one. I really hope he changes his mind.