This is a supplement full of encounters for Pathfinder/D&D 3.. I'm reviewing it on that basis - if you're looking for D&D3. encounters, is this one a good one?
It's certainly unusual - far more atmospheric than your typical collection of monster encounters. The "haunts" described in the PDF are more like traps than like monsters - mystical or occult effects that can confuse, damage or dramatically change a situation at sea, causing mutinies, ships to run aground, or be lost. It gives an approximate "caster level" of the magical effect to see if PCs are powerful enough to overcome it, and each haunt has a way to "break the spell".
CR is approximate in D20, so there's no real use in quibbling over it. There's a weird "XP" entry for each haunt (it's not clear why you would use this rather than CR for a party's appropriate level.) They seem to be more or less right.
The haunts are organized by the type of sea voyage hazard that they express. This is actually very effective - more horror games of all kinds should frame their monsters/ghosts by this classification. What anxiety is created by the haunt? What fears does it provoke or embody? Horror stories make our fears concrete. It's a great help to making my own atmosphere with these.
There are a few missteps in the work - some of the haunts can be destroyed by what would seem like their normal operation. For example, one haunt that provokes a mutiny is permanently destroyed if a sailor that mutinies is killed in the process. It seems like this should instead fuel or preserve the haunt.
However, in general, this is a unique addition to a different sort of "puzzle" encounter, highly creative and very atmospheric. Bookmarks are very well-used, with links to jump to each and every haunt (there are several per page.) Because of the creativity of the work and the innovative organization, I'm giving it high marks.
[4 of 5 Stars!]