To start off, I think it's a great digital piano keyboard. The weighted keys, the texture of the keys, and the weight of the keyboard all plus plus plus. The cost relative to what you get is great.
* The piano and electric piano sounds are very good.
* The sliders and knobs for live control are really neat. Takes a little getting used to but it is a huge plus and lots of fun.
* The direct recording to the USB drive - fantastic! It's such a simple idea but so useful.
* Conceptually, the phrases seem awesome. I haven't delved into them deeply so I'm only going on some observation and light experimentation, what I've read, and what others have said. Programing the phrase on the keyboard is so-so. The real power that I've tested, is in using midi files and converting them through the editor. You can program drum tracks for example, or a series of midi controls over time that just change the settings on the keyboard as you play along in real time.
* The stage setting concept is quite interesting. It's not only a change in patch, but a whole series of keyboard settings. It makes live performance quite manageable
On the other side of the coin:
* The synth sounds and controls don't seem robust. A lot of the instrument samples and generated tones are thin, and seem to be on the middle to lower quality side. The PX-5s is definitely a stage piano first before being a synth. [EDIT] (the thin sounds I'm speaking of are more about the General Midi sounds that by themselves aren't very impressive. Add the layering and effects through stage settings and they become more formidable) [/EDIT]
* The organ sounds could use improvement.
* As I play with the px-5s more, I find some of the physical aspects a bit wanting: the speed at which the keys come up after being pressed is very slow. There are some "work withs" not work arounds per se, that help - the hammer timing and the touch setting - but don't really correct the situation.
* The pitch bend wheel is also very slow when returning to center. There's just a little drag on it that makes it hard to do quick bends.
Overall, it's a very impressive piece of equipment. I get the feel of it being "first generation" of it's type and there's going to be even more great things to come with the next units in the series. I hope to see some changes in the firmware for the PX-5s that correct some of the issues that have been mentioned in various places in the forums. But in the end, this is a well thought out keyboard.
The main things I would want to see improvements on would be the action (control speed and resistance), and the bend wheel speed.