Having watched the whole thing I come away very satisfied. I liked the ending. I enjoyed the flashbacks as much as the present day too, and although I felt the same about younger Hugh at first, I warmed to him quite a bit.
I loved how the whole series was directed by the one man, Flanagan (who did the great Gerald's game) as it really helped set and keep the theme and storytelling strong throughout. I was very impressed by it all in all, I don't want to get into details for those that haven't watched but I would urge you to check it out.
PS:Theo is very hot indeed.