This is a nice soft cover, perfect bound collection of mostly OGL and a couple 4E baddies-- each with a hearty helping of "fluff," in the form of background, lore, physiology, society, and then something specific to the monster. For the centaur this was equipment and medicine. For cloakers, it was psychology. For the maened, this was religion and the derro gave us a very cool set of incantations to play with later. The text is decently edited, and reads well enough that you forget this is a book with over a half dozen contributors, rather than the work of one author.
Then there's all that delicious crunch to go along with it. We get feats, crafts, poisons, and of course, with every entry, a fleshed out stat block of an example that puts the material through its paces. The bargest would make a good reoccuring lieutenant or low/mid-level primary villain. A great story arc could be focused on the liches and an entire campaign could be based around the phantom fungus. It's great to have all the material from nearly three years worth of magazines compiled into single book. The two new entries-- the half-giant and the retreiver are excellent additions, providing an OGL take on a closed content race, and putting an interesting spin on a monster that never quite got the proper transition from its Planescape roots.
My only complaint about this book has to do with some of the artwork. Many of the primary pieces for the entries were either in color in the original publications, or slightly smaller. Now the pieces are either too dark because the original color image was simply printed in black and white, or slightly pixellated. Both are frustrating, because I know the art looks good on the PDFs, and probably in the PDF of this book, but it's not done justice in the printed book. I know there are difficult choices to be made for small press print runs, but I think that the images should have been converted to more legible black and white before the print run, or we should have paid the extra for the color plates in the interior.
Overall, I'd recommend Ecologies, but mostly for the OGL player and those 4E players who don't mind doing their own conversion work. It's a tough sell for the time-pressed 4E crowd with only two entries-- they might be better served purchasing KQ7&9. For the OGL crowd, it gives you some great twists on known creatures and plenty of time-saving stat blocks. This is definitely a nice purchase for you.
EDIT: Having seen the price for the color interior @ http://www.lulu.com/content/-
, you could have the PDF and the print for the cost of the color Print copy. Wow! Something to consider...
[5 of 5 Stars!]