I first read soul hunter, to me that was a very positive surprise, also liked blood reaver, in Hellsreach I found the BT very 2-dimensional, but still enjoyed the book. Liked void stalker, but less than the other NL books, I guess I felt the loyalists are described as tight-arse cunts, certainly if you read how Sevatar is described, WTF. Anyhow, the emperor's gift was very solid as was betrayer, but also here the UM did not really impress in any way.
For me he is a great writer (at the same level as C. Wright), but he will only be superb if he can describe a loyalist which gives me the same feeling as e.g. Talos, Xarl, Sevatar, Kharn, ... (except Orfeo, he was interesting for about five minutes, until he got the end which one would not expect from the future prince of Khorn , a clean warrior's dead).