I'll do a section at a time and will not be copying anything from the document so having your own copy may greatly enhance your understanding of what my comments mean.
Since this is only from a quick read and not from play experience it lacks some perspective playing would provide. With that in mind I intend to come back to blog about how it plays if/when I get the chance to give it a thorough going over with the dice.
Here then is the notes I made while skimming the Bestiary included in the playtest materials.
Creature saves – instead of giving them ability scores, how about a single save score which can be modified according to individual creature through varied situations at the DMs desire.
Same with their skills, just assign a score and don’t complicate things by making it derived from stats.
Monsters shouldn’t be treated like characters.
How do you identify the creature’s level? I see no sign of level or hit dice in the stat blocks.
Calling rounds turns is confusing for players used to turns being 10 minutes. It also is not D&D-like, except for those only exposed to 4e.
Bushwhack seems somewhat overpowered. Is it single use or if the creature remains hidden (does invisible count for this?) does it continue to get the bonus?
The DC for centipede poison saves seems too easy to avoid.
Creatures with spells should not be treated as PCs with regard to flexibility in slot. This creates too much for the DM to remember. Set it and forget it so the DM has one less decision in play and can instead make such decisions ahead of play time and not have to read the unnecessary text during the encounter.
Cunning Tactics also seems somewhat overpowered when it comes to extra damage. Having allies being able use advantage already increases the likelihood of extra damage without that option. Combine Cunning Tactics with Dirty Tricks and you have a recipe for large amounts of damage. Low level characters should not have deep buckets of hit points to begin with and their traditional low level enemies should not be a danger just based on damage potential.
The Corrosion ability listed with the Gray Ooze sounds nifty. The concern is that this may add another element to keep track of which can be forgotten or overlooked.
Pestilence under Dire Rat doesn’t model disease well, instead making it just give extra damage on an attack. Not d&d-like.
Under Stirge, the Attach ability includes an extra die roll to avoid attaching. If it hits it should attach and not eat up extra time with the roll.
Blood Drain under Stirge is problematic by forcing the tracking of a condition and being deadlier that traditional Stirges. If 3 Stirges attach it is instant death.
Troll regeneration is the same as 4e. It is workable, and may be good due to simplicity, but doesn’t feel much like the traditional troll.
The Wight’s Enervation is interesting. Instead of having to recalculate everything after losing levels or having to keep a folder with earlier character sheets, it nicely avoids this issue by using temporary maximum hit point status. Unfortunately having all ill effects go away after a full/long rest weakens the fear that these undead should generate and takes away the need to make important and tense decisions the older versions resulted in for characters and players. Give some real permanence back to the loss while having clerical means to fix the problem and the fear comes back without the book-keeping issues for losing levels.
Need more details about how long after death a zombie victim rises as a zombie. This is a flavorful addition to an old standard bringing them a little more in line with pop culture in a way that doesn’t take away from them being a D&D staple.