karma~ is my ‘dream sampler’, so pretty happy with it, hehe.
The one weak spot it has, which isn’t so much a concern for me personally, is syncing. Towards that end I know @CrackaAttacka is working on a whole sampling/looping toolkit which should be mindblowing. (essentially a lego kit version of karma~ and related tech/tools).
That being said, my main interest in samplers is:
varispeed (recording/playback)
position/window playback parameters
overdub/replace modes
There’s tons of kickass features in things like the Oberheim/Gibson Echoplex (and subsequently SooperLooper), like multiply and things like that, so that stuff is worth looking at too.