This was a better episode than the last two, in the sense that it returned to the main storyline but, overall, the story is just not gripping enough. We've watched many more exciting two-parters over the last 25 years. And, in general, this season just doesn't have any '25-year-old-anniversary-special' feel to it in the least.
I would have expected a long, complex storyline that for some reason involves either revisiting old cases or the brief return of classic characters. But none of that. Instead, we have a story that, so far, seems as if it could have been much more concise in a two-parter. Which shows, as I've written before, the inability of the writers to work effectively on long-term storylines (e.g. Main characters' backstories are often weak or inconsistent). Here, we have scenes that look like fillers-in or new subplots in episodes that put the main storyline in the background. Killing time, really.
It's quite disappointing that Sam Ryan has turned out to be, not someone who would work with The Lyell to solve an unusually challenging case, but just another suspect, like the ones the main characters are dealing with in every case. Her screen time has been regretfully little.
One more episode left of this, and I hold no high hopes, despite my best wishes for the contrary.