If Silent Witness continues, it needs to either reinvent itself entirely with a new group of writers able to write complex storylines or to return to its corpse-of-the-week two-parters, which is its greatest strength. No more longer ongoing storylines, they're just not good at this. (I repeat - whatever happened to Nikki's American boyfriend?)
Anyway, more to the point: this would have worked much better as a two-part story, by removing all the unnecessary subplots or the slow, unnecessary scenes filling up time. It feels as if they were offered a six-episode story, then realised they didn't know what to do with the format. A wasted opportunity.
Other shows have excelled with this format. For Torchwood, after some pretty average seasons, they produced the brilliant six-parter Children of Earth. Even the most recent mediocre Doctor Who got much better with the six-parter Flux.
I mention sci-fi series here because one of the curious things about this season is how it almost ventured into science fiction (DNA manipulation/fabrication?). But Doctor Who is also a good example on how to do an anniversary: a story that is larger than life, with many classic characters returning to contribute to the plot. In the case of SW, that could have been an unusually complex case that requires the help of Sam Ryan, Clarissa, Tom, etc. Or a copycat killer reproducing crimes previously dealt with at the Lyell, having some kind of obsession with the institute's history. Or something like that.
None of this materialised here. We got a typical SW story (and we've seen more gripping ones) stretched across six episodes, slowed down, interspersed with other cases and subplots that just didn't fit together. Plus, it seems like Simone is leaving the show as well, after only a few cases, right after the previous guy (name?), who left after two stories?
I don't know, it was nice seeing the characters back onscreen again, but they need to either revert to traditional, conservative SW storytelling or really work harder when trying new formats.