I've been spending time trying to get more intimate with the sample libraries I already own, and I realized that with the bar being raised so much in the last few years, it's really hard to use sample libraries that don't have all the current technology/programming--they appear very clumsy in comparison. So I was thinking, what are your personal standard when it comes to buying a new library? What features must it have so you won't feel cheated?
For me, I would say:
Alternation/Randomize for repeated notes - This one is a huge one for me. I can't stand patches without it anymore after having used ones with it. It just does so much for the natural and organic feel of your playing.
Portamento/slide - This one is a huge headache for me. So many instruments can benefit from having it, but so few libraries actually have this feature. With it, new life could be given to old samples, without it, samples become static.
Velocity switching - Almost all instruments change timbre as the volume changes--velocity switching (along with filter modulation) is absolutely necessary to capture that nuance.
MOD wheel controlled patches (velocity, vibrato, filter..etc) - It's the ONE controller than almost everyone has readily available, yet so many sample libraries don't use it. I don't understand why.
4 velocity layers minimum - Any less and the patch starts to sound very limited. Drums in particular need this as the timbre of drums changes so much with the amount of force you apply.
Basic effects built into sample player (if it has its own player), for at least a preview of how patches sound with effects while you are composing/jamming--even if you don't use them for the finalized recording.