Agree with that, but then there's only a few things to wrap up and not sure how it could be extended to a full episode. Might have made sense to have a montage at the end of the final episode with text like they did with Line of Duty to very quickly tie up the loose ends.
On this though, some of the performances are pretty good. Idris Elba manages to display the inner turmoil he's experiencing quite well and Neil Maskell has always been a very talented actor, and shows his dark side here.