When I first loaded Assassin's Creed (Steam version) I immediately noticed something was very wrong. There was some odd "pixelization" on parts of the screen.
Take a look at this (once image comes up, make sure to click to show the image in the original size, otherwise there will be scaling):
Take a look at how the bald guy fighting Altair the left is nice and crisp, but the soldier in the background on the right is all blocky. Notice how the table is crisp on the left and become very blocky as you move to the right. This isn't an AA issue, this goes beyond simply jaggies, those are huge pixels in the image consisting of multiple true pixels on screen; and there's pixelization within textures.
At first I thought it was a depth of field effect going wrong. I tried changing all of the settings, Post FX, Graphics Detail, etc. but none of them got rid of it.
The more I looked at it, the more I noticed the pixelization was happening in a very specific manner, take a look:
Everything to the left of that line is fine, everything to the right is pixelized. Look at how Altair and especially the ground texture, goes from sharp to blocky as you move across the line.
It's not too obvious in a static image, but in motion is REALLY stands out. You can see this clearly defined line along the diagonal where as stuff moves across it, it become pixelized.
My specs are:
Athlon X2 FX-60 (2.6GHz)
GeForce 8800GTX on 174.74 drivers
Windows XP (32-bit)
----update with collected information----
This issue only happens at certain resolutions and only in DirectX 9. It occurs regardless of any graphics settings, it's totally dependant on the resolution.
The standard resolutions that it occurs at are 1360x768 (native res of many HDTVs) and 1680x1050 (native res of many widescreen PC monitors).
Upon further investigation, since the game is locked to 16:9, it seems that it occurs at any resolution where the height of the correspondig 16:9 resolution is in an odd number. E.g. the 16:9 viewport for 1680x1050 is 1680x945 - odd height. Although 1360x768 is close to 16:9, it's not exact, the exact 16:9 is 1360x765 - again odd height. If you setup custom resolutions that would similarly result in an odd height, they have the same problem.
All other standard resolutions result in an even height at 16:9 doesn't have the problem.