Of course, "Greatest Hits" is not equivalent to "Best of". The Sister's strength was in creating albums that were full pieces of music, to be listened to as a whole. Take songs out of context and the recording suffers a bit. Also, many of the best songs were never released as singles (Marian, Floods I and II, Some Kind of Stranger... off the top of my head), so of course, they don't get a look in. Finally the track list is in reverse chronological order, which will give a bit of a skewed listen to first-time experimenters with the band.
But.
Let's face it, all the songs here are, individually, very good. It's weird to hear tracks from such differently orientated albums juxtaposed together, but it's a great record to stick on in the car and just revisit a selection of the Sister's fine (if not finest) tracks. Advice though, if you know you like the Sisters of Mercy, just buy all the albums, they're all worth it :).