I do not like Cameron Diaz. I really don't. (My opinion but) she can't act and her face is often frozen in one expression no matter the emotion. Despite his personal life I probably couldn't care any less about than I already do, I think Tom Cruise is a fabulous actor.
Knight and Day was a funny and enjoyable movie. The middle seriousness needed to be cut, it wasn't a serious movie. It was all in jest, all tongue-in-cheek and it should have stayed that way.
I was a little annoyed with the parts when either he or she were knocked out and it was a weird drug-induced montage about what happened in the interim, but alas. I guess they didn't want to...slow the story down? No idea, it was weird. However, other than that saggy middle problem, I think the humor was dead on, it played to, off of, and made fun of a great many spy movies.
Probably why I enjoyed it so much. So no, despite my utter dislike of Cameron Diaz, and the fact that the middle needed re-editing, I do recommend this. Just remember to take it as it is and for what it is. Completely irreverent.