By chance I got to play a Yamaha PSR-E363 and was hooked the moment I switched it on and heard the grand piano sound after pressing the smooth velocity sensitive keys. Previously I'd only played older Casio and Yamaha keyboards and whilst fun the sounds, particularly the piano sounds, were ok they were nothing compared to the E-363.
After playing keyboard I decided to investigate and looked online at prices and specs and decided on the PSR E-463 as it has a few features the 363 doesn't. I wasn't sure whether I needed these extra features but the ability to have some control over cut off and resonance swung it for me.
I think in hindsight the E-363 would have been a better option for me as the aforementioned cutoff and resonance controls do affect the sound but in a quite limited way, certainly not as much as on most dedicated synths. There are many features I'm unlikely to use but can see them being very useful to someone composing (it is billed as an arranger keyboard anyway). So if you're just looking for a great sounding keyboard my advice would be to spend a bit less on the E-363 as I believe it has pretty much the same voices.
As for using it like a regular keyboard with an array of voices, it's great! I think the keyboard action is smooth and the keys, though not to the solid quality of a real piano or a higher end keyboard, have a quality feel to them and I think this is where Yamaha have the edge on Casio. The sounds/voices on the E-463 are a mixed bag ranging from very good to excellent. Grand piano, strings, most of the organs, sax/brass and harmonicas are the standouts for me. The synth sounds are ok but having subsequently played a Casio at a similar price point I'd say the Yamaha voices just aren't as good. But overall the voices are brilliant; like having a music store at your disposal when recording.
Like other Yamaha products I've used, it's smoothly and solidly built and I can't see it having any reliability issues. I'm very pleased with it, enjoy playing it (though I'm not a great keyboard player) and am finding it a useful tool in my little home recording set up.
In conclusion, it's a very versatile, relatively inexpensive but good quality keyboard that packs in some wonderful voices and masses of features; whether you need them all depends on what you want to use it for.