I've had my eye on this for a LONG time and after reading countless reviews and watching every YouTube video available, I finally bought my own copy. WOW is all I have to say! NI really outdid themselves! I was skeptical about buying a virtual piano but am not disappointed in ANY way. The touch, expression, and fullness (along with a good set of monitors or headphones) will have you feeling like your playing the real thing.
The overall sound is perfect because of it's imperfection. Anyone who's ever spent time with an acoustic piano knows that even a 'perfectly' tuned piano starts to sound 'out of tune' the lower or higher you go on the keyboard. I don't know all the technical reasons for this, but I've played digital stage pianos that don't sound quite right and I always end up figuring that it's because the notes are perfectly stepped from one another. They don't have that harmonic resonance you get from the real thing.
The sampled pedal and key noise is exquisite. I was recording an artist who said to me, "WOW! I don't know what it is, but I keep thinking I'm playing a real piano!" Then I turned off the 'noise' and she said, "I don't know why, but it doesn't feel as real anymore." When she came back into the control booth and I showed her that she was actually playing through a software program she couldn't believe it!
I typically don't use the convolution reverb (since I like to run all my tracks through the same verb send), but it sounds amazing as well! It's a wonderful tool to have when running in stand alone mode. Having a nice Hall verb really gives you the feeling of writing your music on a Yamaha C3 Neo that just happens to be sitting on a renowned concert hall stage.
I have 2 midi controllers that I use; one that has 88 fully weighted keys and one that's just a 49 key, synth action board. When I close my eyes with the 88 key controller, it's easy to imagine playing a full grand piano. The thing that really surprised me was that I got the same feeling from my 49 key synth controller! If that isn't a testament to how full and rich the sound is, I don't know what is!
It seems to me that this particular piano sound is geared toward R&B and mellower type music. I'm not saying that it couldn't be used for other genres or styles, but I think NI has other virtual pianos that have more of that tight, pop sound that a lot of people are looking for. This piano has a darker sound. I'm sure you could use EQ to get more top end, but in my opinion, it takes away from the natural tonality of the piano.
One more little note before I wrap this up. I'm running Alicia's Keys on a 2.4gHz Dual Core Mac Mini and haven't had a single problem with CPU usage. Even when running it through my DAW (Presonus Studio One Pro 2) I've never experienced any performance issues.