Consider Phlebas is generally considered weak but good as an author first sci-fi book. The plot is not particularly strong but the prose remains enjoyable (which is notable in a genre plagued with authors who basically can't write). The fact that it is amongst Banks worst book is a testament to his quality as an author.

I have never seen it actually recommended. The Player of Game is the first really good novel set in the Culture universe and most of them are good from there on.