Just watched this video of a friendly, if not slightly geeky, guy reviewing the Alicia's Keys sample library. REVIEW - Kontakt Alicia's Keys piano samples based on Yamaha C3 Neo Video
Sounds fine to me. I rather like it. I play on a 9 Foot Bluthner regularly and I think the Yamaha sound is a great alternative to the german pianos or even a Steinway.
Regarding velocity, there are plenty of velocity curve offsets in the program and most keyboards have velocity curves as well that you really need to play with in order to take advantage of sample velocity switching. I absolutely hate playing certain piano sample libraries on my M-Audio Axiom. The non-weighted keys and the velocity curves in that keyboard make it really hard to get the middle velocity samples to play. It goes straight to 127 really fast. I play the same sample libraries on a weighted keyboard like a Yamaha CP300
or my old Korg SGProX and all the sudden the samples sound and feel amazing. Play around with the velocity curves to calibrate it to your keyboard. That's the reason they have them. Every keyboard is different and so is every player. If you're heavy-handed, then you'll need one that makes you really have to dig in to access the high velocity samples.
Regarding latency. I don't have it so can't comment. That can be a real deal breaker if you don't get it resolved. The video review guy is doing some fast runs and it doesn't seem to exhibit latency probs for him. Sounds like a classical player so you figure he'd be picky about that too.
Hope it shapes up for you and gives you what you were wanting it for.