navindra The funny thing is, if you pick any any regular piano, and you play a single note, you may well find the sound of that single note is intensely ugly all by itself
Interesting observation. Over these last few weeks, I finally start to get why I/we am/are easily fooled by VSTi piano demos/videos into thinking they sound wonderful or at least quite acceptable, and perhaps then even buy them and are disappointed the moment I/we start playing it ourselves. (Resulting in virtual landfills full of piano libraries, as some of us have.)
I think I learned this from purchasing and using a Black Friday NI Noire license. From videos, e.g. by @Gamma1734 and Simeon Amburgey, I got interested in it more than a year ago. It was almost going to be my first paid virtual piano, hadn't it been for @David B showing VI Labs' Modern U on PW and me stumbling upon the thread he created. So I started with Modern U instead, which is rather fortunate: had it been Noire first I would have stopped my virtual piano attempts right there and then, while Modern U surprised me in a good way and gave me "something useable" and even inspired my two layer/two amp/six speaker setup which is quite enjoyable. All in all I learned a lot of valuable things from that whole integration process.
Back to what navindra said. So these last weeks it occurred to me that a virtual piano is a lot sooner acceptable or even nice when pieces with many notes and richer harmonies are demoed, concealing the imperfections and sometimes (or often?!) downright ugliness of individual notes/samples. But when really listening to what a virtual piano has to offer in pure, real per-note beauty, many or even most of them sadly fail in real life. To me this becomes obvious rather quickly, because I can enjoy just playing a key and listen to what it gives, enjoy a beautiful sustain and release all on its own and so on. I also like to experiment with minimalistic music such as "Spiegel im Spiegel" by Arvo Pärt. Making such a piece sound really good for its whole ten-minute duration is a true test for instrument and player alike. Playing Modern U, this (generally) works very well because (most of) its notes/samples sound truly lovely -- individually as well as in harmony and resonance with eachother.
I like Noire for its gorgeous low end, up to close to middle-C. In that region, I like its low region more than in almost, if not all, other libraries. However after first install and first playing using the defaults, I was truly shocked and thought it an immediate write-off. Not willing to give up easily I worked it and worked it and worked it some more and now have a preset that makes it as natural as (I think) it gets*). Yet, apart from left of middle C or thereabouts, I don't really enjoy playing it because -- and here this long ramble goes full circle -- the individual notes right of middle C just don't stand their own ground in sounding a beautiful piano. (So now I use Noire with a touch of its interesting sub-bass "microphone" to figure out double pass pieces and then take what I learn to my (not-yet-double) bass to play. I find Noire surprisingly useful for that, but won't use it as a piano very much -- if at all).
Long story short: if a piano, real or virtual, isn't capable of making individual notes sound lovely, it lacks the essential basic integrity to make music, however minimalistic or complex.
Cheers and happy selecting of instruments of integrity,
*) In @Frédéric L 's great comparison work, he included two Noire renderings. The second one is based on my preset, I think, or at least something sounding very close to that.