The first book (Neptune Crossing) is truly amazing, and I'd give it 5 stars. The entire science fiction flair stems from one really unusual alien live form and an extremely powerful and mysterious machine, but this is more than enough to deeply capture the reader.
The other two books, unfortunately, are a big disappointment. They feature tons of aliens and alien machinery, but they all act just like some random guy you'd meet on the street. In contrast to the first book, the aliens don't appear alien at all. In addition to that, the actions of the party that gathers around the protagonist seem totally without reason (unreasonable as in stupid, and not as in alien, that is). Moreover, the main storyline in book two is never truly resolved, at some point the "problem" (whose nature never became clear), is basically just declared as "solved".
The author occasionally switches perspective to some of the other characters, but these episodes are so short that they don't really give any insight into the character but just interrupt the flow of the book.