Honestly, episodes 1 and 2 are the lowest points in the series.
3 and 4 are marginally better
5 is taste dependent, but generally thought of as shit.
6 and 7 were okay.
8 and 9 introduced GAR into the series
10-12 were good.
Season 2, starts off with a bunch of decent and filler, then starting when Kana is revealed to the other dolls, and challenges them, it becomes more serious. The second half was worth whatever one would have to endure of the first season, ending was a cliffhanger that was never picked up.
And then, you have Ouvertüre. Brilliant.