These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Everyone Is Jesus in Purgatory: Literally. When Gene starts to remember who he is, he describes the world the series is set in as "Somewhere we go to sort ourselves... Coppers." Nelson (from Life On Mars) is the gatekeeper, and Gene guides lost souls to him.
Foe Yay: Gene and Keats. Gene and Supermac (sauna scene anyone?). Also Alex and Keats.
Growing the Beard: With some exceptions, series 1 in general has a much more frivolous feel to it, particularly in the behaviour of Alex's character. The drama gets much better when she becomes more the serious police officer from series 2 onwards.
Harsher in Hindsight: In the very first episode. Remember how confident Alex was about Getting home to see her daughter and "I am not going to die."? Yeah...