Great action, decent sound
I purchased the Kawai MP8ii to start "re-learning" to play the piano again. Prior to this I had an older Roland EP-9 which did not have weighted keys, so I knew I wanted to upgrade before starting serious practicing.
I did not have access to this unit to try it out, but the store did have a Kawai CA-51, which uses the same action. Based on that, I bought the MP8ii and have been very pleased with it since. Before this I also compared it to the Yamaha CP33 and the Roland RD700sx (not the gx) and felt the Kawai had the most realistic action. I've read in other forums that the MP8ii has a slightly lighter touch than the original MP8. One of the Kawai reps is quoted as saying that the weight is actually the same but they've reduced the friction of the action.
The sound quaility is excellent for my purposes. There are no built in speakers so I usually practice with headphones - Audio Technica Professional Studio Monitor - ATH-M40fs, which are awesome (response is flat from 5 to 28,000). I also use some powered speakers - M-Audio BX5a, which are decent too, but not as accurate as the headphones, of course.
It doesn't have some of the bells and whistles of other units, such as arpeggiators and sequencing, but that's not the point of this unit. It has MIDI and USB so it's easy enough to hook to a PC to get those functions in software.
Overall I am very pleased with this unit and would buy it again in a heartbeat. I imagine it will last me a very long time before someone comes out with a keyboard action that is enough better to warrant an upgrade.