I'm playing a Knight in a pbp game. My first impression with the Knight was negative, but I decided to give it a try anyway.
The few things I dislike is the Shield Block "Dodge" mechanic he gets, I dislike Dodge as well actually. I just don't think its worth tracking and think it should just be a bonus to AC.
The other thing I didn't like, was that, with Bulwark of Defence, the area around the knight is rough terrain for those who started the round threatened by the knight. When I originally read it, I missed that part, and was disappointed to learn enemies can still just run past the knight.
Also, I think his higher level abilities need more... power? Loyalty beyond death is a little underwhelming for something you have to wait till 20th to get. Impetuous Endurance is neat, but hardly something to jump up and down about. Rolling a 1 is statistically rare, and generally speaking from the campaigns I've been in, the ability would be irrevalent, as I'd fail anyway.
I do enjoy his Test of Mettle ability. Also, I like how violating his "code" isn't some game stopping event.
Overall, I'm enjoying playing the Knight. But, I forsee problems in the higher levels, where PrCs are more available, and the Knights class features are less appealing.
Hope that helps.
Grae