Everything everyone is saying about this one is true. One thing to add: it's a lot for a single sitting. It runs almost four hours. People couldn't have had an option when it was transmitted on telly - they had to wait for the subsequent episodes - but when you rent or purchase it now you can't be forced into that option - and you'll find it nigh on impossible to break things off at the hour or two hour mark - it's just too good as everyone says.
Perhaps the best news is that Lynda La Plante is back. Episode two wasn't bad - but it wasn't La Plante's writing and it didn't have her magical hand on it. This one does. It's as if she took all the stuff she found out worked in the first episode, concentrated it, and flung it back. Everything is deeper, grittier, gorier.
There are seven huge episodes in this opus, all told twenty two hours of viewing. So to single out any one episode and say it's 'best' is going to be difficult, but taking only the first three it's not hard to see which excel more than others, and this one has to rank right at the very top.