The show, as a whole, started to go downhill. However, there were still great moments here and there. The finale was absolutely horrible.
I hated Robin throughout the entire series and do not find her character attractive. She looks fine, but her personality and character as a whole are repulsive. However, I liked the build-up to marrying Barney and thought the entire thing was a good payoff... only to be completely thrown out the window in the finale.
Also... Marshall's critique on Inigo Montoya is fantastic.