I agree 100% that the HALion 6 strings and brass are pretty terrible, and of course I'll never use them. If you're looking for a sampler/hybrid that has great libraries that comes with it or you can buy--HALion is not for you.
What makes HALion 6 special is that it has tools to automate making your own sampled instrument. For example, you hit one note, pause, then the next note, pause, etc. and HALion makes all the files, names them and arranges them on the keyboard to build your (basic) instrument. And if you want to share that instrument, HALion also comes with a host of knobs, sliders, buttons, etc for you to make your own interface. Very intuitive--drag them into place, and then assign their functions in a way similar to using MIDI learn. You want a picture? Drag one on.
These instruments can be exported and played by anyone in the free HALion Sonic SE player available on the Steinberg site.
For those who don't know, HALion a hybrid sampler/synth that allows you to combine 4 layers into a "program" (preset/patch) There are 5 possible layers--synth (including typical analog, but also wavetable & granular), sample, instrument, drum, and sliced loops. You can then assemble up to 64 programs into a multi. So when you're judging, for example, the two pianos that come with HALion 6, perhaps it makes more sense to think about how they can become elements in complex hybrid sounds, rather than to compare them with your favorite Kontakt piano libraries (where they probably lose). They are decent, but they shine in preset multis and the multis you make yourself.
There are also many synths in HALion that I think are quite good, particularly the wavetable synth Anima, the granular synth Auron, and the moog-style Analog synth Voltage. You're meant to layer this stuff up in HALion 6.
I haven't been exploring HALion that long, but the third thing that has my attention is a very intriguing arpeggiator-thingie called the Flex Phraser. If you have Cubase, you may have noticed it in HALion SE instruments like FlexPhrased Folk Nylon. In fact, every guitar sound that involves strumming, arpeggios, or finger-picking in HALion SE uses the FlexPhraser. With HALion 6 you have an enormous amount of flex phraser arps available for guitar, piano, bass, strings, drums, etc. in various genres.
All of these can be assigned to any instrument or layer and can be adjusted. The flex phrasers work in two ways. If you hold down one key they play something like a strum or a riff or an arp. But if you play chords it follows your playing, no matter what you play (no limitations on chords). Although I have many guitar apps, I find the flex phraser strumming and picking to be the most playable I've ever found. As a guitar player I tend to be constantly changing chords and a lot of libraries choke and stutter unless I make changes on the measures. The HALion stuff is the first time I've ever got a guitar VI to play the way I want it to. And there are adjustable dynamics built into them which make them more realistic. If you don't like the HALion guitars, the Flex Phrasers can be saved as MIDI files and used with any instrument you like.
If you have Cubase, try the Halion SE guitar picking and strumming and see what you think.