to create realistic midi renders for the midi files project, i needed a realistic guitar sampler and, after a little research, decided this was really the only option. technology moves so fast that this may no longer be true, a mere year and a half later.
what i found was that the other options either come with baked in effects or were broadly generative in nature. baked in effects are great if you're basically a piano player and want the guitars to conform to a genre style. so, you see these libraries with guitars categorized with terms like "pop", "blues" or "rock". for a lot of people, that's really enough, and that's fine.
but, i needed it to be as basic as possible, so i could shape my own signal path through guitar rig or whatever else. i wanted the cleanest, most bare samples possible - just the most basic DI sound of picking a completely clean guitar. and, for me, that's actually true, broadly.
it has some issues - it can be a little choppy, and it's maybe a little bit *too* realistic in some ways. alternate tunings would be useful, if they don't want to let you pick notes that would otherwise be impossible to play.
keeping in mind that i'm going to play live guitars for virtually everything out of principle (because i'm a guitarist), this is of such limited value to me that it's not really worth my time to find something that fixes these limitations. but, as a specific tool for the specific project i used it for, i was very surprised by how good it could sound through some effects.
http://www.musiclab.com/products/realguitar/info.html
https://www.musiclab.com/products/reallpc/info.html