I think to be HALion is intended to be used as a layering instrument. It's not so much about the individual sounds IMHO as it is about putting layers together into a multi.
So you can combine sampled sounds, wavetable, granular, analog, organ sounds, filters into one big patch. You can add in a sophisticated arpeggiator, the FlexPhraser into any of the layers, and there's then all the usual filters and effects.
So a lot of people just look at the sampled sounds and find them inferior to the ones they have in Kontakt, and give it a pass. But it is extremely powerful and can give some amazing sounds when you put its components together. It's amazing with sound design, but equally good with one-person-band types of patches.
I think it has more in common with Falcon and the Multis in Omnisphere. I'm not saying that it has sounds as good as Omni, but it is easy to set up layers and complicated splits. And Omni just has samples of synths, while HALion contains real synths.
HALion is a beast if you unleash it.