I feel like the offensive line apologist for this site, but this O-line is tops in the league. ProFootballFocus has the Chiefs having the 4th best line:
Offensive Line Rankings: Week 10 Update | ProFootballFocus.com
I consistently watch (and re-watch on NFL Game Rewind) and see the line blocking well. It takes a beating by the casual observer when our QBs (Cassel especially) are back there, the first read is covered, and they have no idea what to do.
This is also worth a re-post (also from ProFootballFocus)...
Cassel takes the 7th longest among all QBs to get rid of the ball (on average 2.83 seconds). However, he has the 5th best number in the amount of time it takes before he is sacked (3.78 seconds). This says a lot about how well the line is doing, despite the poor QB play.
Simply put, when you have a QB who can't go through his progressions, it's a recipe for disaster when his first read is covered.
I thought that this line would get destroyed by Von Miller with backup LT Donald Stephenson plugged in. Miller ended up with 1 sack and no other QB hits.