I've been a LOM and A2A fan right from the word go, and this series, for me, is probably the best yet.
It's got the darkness and grit of Life On Mars, but still manages to keep the crazy 80s vibe which I loved in the first series of Ashes To Ashes. But the thing I love about it the most is the development of the characters, especially Chris and Ray (giving Marshall and Dean a chance to flaunt their skills), Alex's increasing dependency on Gene, and the issues this leads to, and of course Alex's continued battle to get home.
Philip Glenister and Keeley Hawes really do shine together, and the more grounded, level headed Alex we see in series 2 is even more likeable than her series 1 persona, and the emotional development in Gene really does show what a truly complex and above all, human character, he is.