Very helpful in giving me inspiration for my own templates in my campaign.

There's some value in this, but it could've been much better too.

The best part of this product are the ideas for actual gameplay differences under each template, the ideas for things your monsters could be doing. They are thematic bonus actions and reactions, and spell lists that get to the point. The product seems aware of the fact that monsters only live a few turns, and thus they have a very short time to be thematic. With most of their new abilities being reactions and bonus actions, those monsters will get to do quite a few interesting things before they are inevitably cut down. It works, and unlike the statistics that you don't need, most of these are ready to be used as they are.

That's about all I can praise though. One negative is that the product focuses too much on the statistics. Other than the bonus actions, the templates do things like "+n HP" on a monster or "+n damage on its attacks", (some templates only modify stats, nothing else) which could be devastating or insignificant, depending on the levels the group is playing at, because these amounts make no attempts to scale with CR. As a result, it's completely useless information, as you have to determine those amounts yourself anyway, tailoring them to your monsters. Some templates are more useful than others, and some templates are better thought out than others. There are specialty wizards and psi-users I don't think anyone will ever use, and there are some variations on the same theme that feel like padding.

There is no lore or description with any of the statblock, which is a shame. I would've liked at least some description of their strategies. That would help with making these templates ready to use right out of the box.

The layout and the graphic design is a mess. The templates themselves are fine, but they are sometimes awkwardly broken up in the middle of the text to continue in the next column. The book is also littered full of inconsistent art. Some of it is colored, some is black and white. Some of them are too small, some of them are too big. Most egregiously, some of the art is stretched or squished, which is a huge mistake. The result looks ugly and amateurish.

There is also no index for easy searching, or a print-friendly version, which is annoying.

In conclusion, there is some value in this product, no doubt. If you want a special enemy in your encounter and you want it to do some cool stuff during the few turns it's going to live, there are some good ideas you can adapt from Liber Varietas. However, there is quite a lot of dirt to dig through to find those little nuggets of gold.

The 50 templates found within will certainly change up your monsters (although I personally find they really work well for NPCs more than monsters), and the few example creatures at the end are nice, but I dislike the focus on statistics over narrative. There's no narrative content contained within this book, where giving little examples of how to use these would've been appreciated not because the DM can't figure it out but because it would break up the content to make it easier to consume.

I would also have loved to see a chart or index, giving the name and page of each template as well as a chart showing the XP change when increasing a CR. The CR adjustments I see in here all seem to be relatively following the DMs Guide but any instance of damage I would have reworded. For example:

Overhead Strike, triggers opportunity attacks from creatures within 5ft who are not prone. Deals an extra xd8 damage. X is equal to 1 + half of the creature’s challenge rating (rounded up). If the target is prone, it deals an additional 2d8 damage.

To me, that 2d8 could be super significant at lower levels and I'd instead suggest something like "this deals an extra die of damage, or two extra dice of damage against prone targets". Although I don't consider that a deal breaker. Oh another recommendation: remove the word "new" from everything. "New Ability" "New Reaction"... templates are designed to add new things, this is just an extra word that isn't needed.

Overall though, totally worth the price.