I don't want to talk too much about his music, because I want you to feel his world yourself, and I don't want to spoil it.
I first encountered Mertens' music in early 1980s when he was involved in the earliest (and the greatest) times of Windham Hill label (e.g. 'Close Cover'). After many years, I re-encountered to his music this time with this great album. In short, this album contains two of his greatest pieces, namely 'Whisper Me' and 'The Fosse'. I think they are masterpiece. You can hear some previews here so maybe you want to try some. 'Whisper Me', for example, is so atmospheric that in my eyes I can automatically see some scenery that would appear in films by Krzysztof Kie'lowski, as it were. It is classical but in a way modern (although not too much), and I enjoy the whole world that starts appearing within myself. Sorry if my review is slightly sensationalistic, but this is the only way I can describe his music, especially this album, because this album is so sensuous to me. Hope you'll enjoy it too.