For more detailed information on a given product please see the review that will report on any weird bugs or issues encountered.
Host: The plug-in used to play the library, if it's VST then it's provided by the company itself, otherwise the plug-in is noted. Kontakt has 2 versions that causes confusion. The first is the paid-for version and many libraries require this. The is denoted by the lable Kontakt. The second is Kontakt free which references the free Kontakt player and means you do not need to buy kontakt to use the library but you must have the free kontakt player if you do not own Kontakt. This also means a library tab will be present.
NKS: is a standard that is useful for native instrument gear, if you don't know what this is then it probably doesn't matter to you.
Phrases: The library has pre-recorded phrases that are interacted with instead of individually sampled "notes".
Leads, Bass, Pads, Keys, Other: A loose judgment on the content of the patches provided, with a general notion of distribution of number of patches provided.
FX Engine: a notable FX engine that gives more control than simply having some basic effects on the screen, typically with some degree of layer control available.
Key Notes: Denotes what key colors do. This can vary a lot, from FX switches, to indicators, to key switches.
CPU 10 Instance: I open my default template with a base cpu meter in FL at 4%. Then open 10 patches in an attempt to represent a normal use case. If the patch can play chords then I give it a triad otherwise I give it the midi that it expects and measure the load of 10 instances at once. This is a very light measure of a heavy load cpu. Take this with a massive grain of salt. I have an i9 10850k running windows 10 on FL Studio 20. The audio interface is a Scarlett 18i20 with a buffer size of 1024.
Build a Patch Option: The ability to manipulate sample content from the provided samples to create new patches.
Preset Style: If it is a general engine then the UI is a more general one that is made in a way that can house multiple sound sources not specific to the library it's in. If it's rigid then it is designed especially for those samples and is unique.
Access to samples: Direct access to the physical samples provided so that a host isn't needed to get to them.
Intuition: A loose judgment on how intuitive the interface is. How quickly you can make small and large adjustments. Every time I have to look something up this score goes down.
Modulation: The presence of ADSR, LFO's and Sequencers.
Round Robins: This just notes if round robins are present, not how many or the detail level.
Sampling Detail Level: If available a general look at how detailed the sampling is on a scale of 1 to 10. Number of samples per note and dynamic levels are the main considerations, along with release samples and other details.
Manual, Tool Tips: Notes if these features are present and may comment on their quality.
Sequencer/Strum Support: Note and play sequencer options, more than just having a sequencer. Access to chords and strum type should be available.
Installation Pain: On a few occassions the installation process was so bad that the library wasn't worth it. Most librarys have streamlined the installation process so that it is not bad, but it is noted here.