I find "a bit saddening" to be a bit of an understatement. That said, heh, yeah, I wholeheartedly agree with you about the slowdown in action.
Date Night certainly has its merits. It was (or is, or could have been) a great way to explore the different character dynamics, their individual characterizations, their characterizations in pairs, and their characterizations as a whole group. ... Unfortunately... wait, do I need to progress past that word?
The other side of this coin is, of course, Vaughan's work that we're coming off of. Not only did he weave high-action, -intensity, and exciting stories, but he succeeded admirably in, at the same time, fleshing out the characters. So, yeah. From Magnetic North to Date Night is a pretty harsh drop.