Full of action is a great exaggeration. As I remember it, the first half of the episode is a combination of the interviews, cop work, Rust's introduction of his plan, stealing drugs and making them. The second half gets going after Rust walks out on Maggie at the diner. Then we're off on the trip to the biker bar and party in the back. These parts are still what I'd consider gritty, and based on video reviews and comments from elsewhere, a show about biker gangs, Sons of Anarchy, doesn't apparently hit the same mark in comparative situations.
I don't understand how what transpired at the very end of the episode turned the show into something that can be described as action heavy. When they get to the project, yes, it's action, a contained 7 minute sequence. It wasn't the majority of the episodes run time. And it isn't the 2nd or 3rd bit of action that has been peppered throughout the episode. General episodes of CSI are comparable? I've never heard anyone speak that highly of that show in the entirety of its existence.
Additionally, from Rust and Marty's interviews, the big shootout, what we thought we were leading up in episode 5 was a lie. What actually happened makes for great gifs, but remains a blunt, abrupt resolution to the capture of the would be criminals.
I think that what happens at the end of episode 4 is absolutely appropriate and needed to be shown. We needed to see the undercover work that Rust has talked about and like I mentioned in another thread, we see it contrasted with Marty who's completely out of his element because he can't dress the part or even act it.