I don't want to be negative about this, but four episodes in, it's hard to believe that it's going to come to a conclusion that (a) makes up for the show's problems and (b) will fit comfortably in Doctor Who continuity.
There's a lot of stupidity, much of it the usual Doctor Who simplistic approach to how governments work (why would the UK PM even be having meetings with senior French and American military figures and no British military or ministerial personnel?), some of it things already mentioned (oh, he's bringing a gift, nothing suspicious about the guy we don't know anything about bringing along a dumb gift). The dialogue... ugh. A lot of the cast are giving it their all but they don't have much to work with.
And the powers the aquakind have demonstrated only make me wonder why, if they've been awake and aware all this time (unlike their Silurian cousins), they let things get so bad. If they could magically dump all of the plastic in the sea back on the land, what were they waiting for?
I thought we might be getting another Children of Earth, but at the two thirds mark, it feels to me like we're a lot closer to Miracle Day.
If you found someone who knew nothing about UK TV in general and Doctor Who in particular and gave them Years and Years, It's a Sin, and The War Between the Land and the Sea, would they be able to believe the same guy who wrote the intense and powerful first two stories also wrote this?