This pdf is 19 pages long, 1 page front cover, 1 page editorial, 1 page SRD and 2 pages of advertisements, leaving 14 pages for 101 monster feats, so let's take a look at them!
The first thing you'll notice is that the layout is beautiful and adheres to the full-color two-column standard set in the Pathways free e-zine line. Thus, the book is a beauty to behold. Monster feats are feats specifically for monsters (d'unh) and not players, so what do I expect from them? I expect them to be an easy, cool way to customize my critters, expand their abilities and open up new and iconic tactics for my tried and true foes. What I don't expect is "Add +2 to the DC of ability XYZ".
Thankfully, this pdf does not fall into this filler-trap, but rather offers some very cool feats for monsters - One example would be the spit venom feat tree, which lets you spit your venom as a contact poison. Poison-lovers do get more love with virulent poisons, but there's more: Fans of our iconic dragons can now give them feats to change their breath weapon-energies (already seen that, sorry) and some rather cool ones that let you sculpt breath weapons into e.g. cubes or spheres and there are some abilities that make swallowing be a VERY, VERY painful experience for the swallowed creatures.
Indeed, many of the feats add free maneuvers to abilities like e.g. pounce or improve these already existent abilities. The true winners of this pdf, though, at least for me, will be outsiders (especially the poor elementals) and undead: Elementals can change into living, fighting Walls (via Elemental Entrapment) or detonate and instantly reform, angels, devils and demons and the like can move to the astral plane and directly from there to heaven or hell via "Astride the Ladder" or deliver a terrible curse when being banished to another plane. "Cloak Alignment" makes for a great feat for insidious/stealthy outsiders that don't want to be discovered via low-level divinations. On the goofy, humiliating and just plain awesome side we also get "Expel Creature", which lets you projectile vomit swallowed foes at enemies. Imagine the look of your players. Priceless.
Miss the Slaadi and their parasitic means of propagation? "Pandemoniac Corruption" lets you add the inside-out-friend-fun on your creatures. Undead gain perhaps one of the most deadly and cool feats EVER: "Aura of Suffering" negates ALL kinds of magical healing, fast healing and regeneration in an aura of 5ft. per HD - if used sparingly, this makes for truly frightening opponents, especially when e.g. combined with the almost inescapable "Death Grip". Liches can now use living beings as phylacteries, serving for awesome moral dilemmas. However, there also are losers - fey get the short end of the stick and e.g. "Beguiling Nature" only adds a +2 to Bluff and +2 to the DC of charming abilities - rather bland, especially in direct contrast to the big, baddy abilities like "Breaching Fling", a capsize attempt that flings people through the air and the "Improved Awesome Blow", which lets you, Sauron-style, bash enemies and fling the through the air like the puny foes they are.
[4 of 5 Stars!]