When reading the plot synopsis prior to first watch, the story did seem very over complicated and far fetched. That was before reading up on the real life case "Immortal" is based on, a complex and harrowing one it is too. This is one of many 'Law and Order' episodes to be based on a real life case, which has often been executed very well indeed and more and then there have been other times where the execution underwhelmed somewhat. Both extremes were present in this season.
"Immortal" to me was excellent. There were many excellent episodes in a final season that was so much better than expected considering the reputations of many final seasons of many great shows, and to be honest on first watch part of me was not expecting this to be as good as it turned out. Don't let the basic premise put you off, it's not near as far fetched or as strange as it sounds and it makes more sense when reading up on the case it's based on.
Like with some episodes in Season 20 and actually of many 'Law and Order' episodes, the final quarter is on the ordinary side.
That is pretty much it though in regard to any criticisms for "Immortal". It is as ever shot with the right amount of intimacy without feeling too up close, even with a reliance of close up camerawork. That the editing has become increasingly tighter over-time is great too. The music isn't over-scored, manipulative or used too much. There is intimacy and tautness in the direction. The regulars are all fine, particularly Linus Roache who dominates the legal scenes with great authority. Lupo and Bernard have grown as a partnership, even if they are nowhere near Briscoe level. Jacinto Taras Riddick terrifies in his role and Seth Gilliam does shrewd very well.
Script is intelligent and lean with no signs of fat. The debating intrigues and provokes thought. The story is securely paced and has some nice edge and grit. It is also very disturbing and sad, and while complex it's not incoherent and it's not far fetched. The legal scenes are riveting and have tension, where it was easy to care for what the verdict would be.
Concluding, excellent. 9/10.