Very nice, but could have been even better!
My first hammer-action keyboard. Though not quite the same as an acoustic grand, I love the feel verses an old non-weighted Roland W-30 I've got. If you tap the keys with your fingernails, however, you probably won't appreciate the "plasticky" sound you get back. Also, the keyboard is a bit noisy, so if you're doing any acoustic recording (e.g. voice or other instruments) with this in play, you might pick up some keyboard clatter. Also, be sure to have a VERY sturdy stand for this monster as those hammer action keys don't feel right with even a slightly flexible stand. I would also have liked to see this cased in aluminum instead of plastic, but it already weights 67 pounds, so...
The LCD display is easy to read, but my personal preference would be to have amber (to match the button and bender/modulator knob lighting) backlighting in the display rather than blue as amber is a bit easier on the eyes in low light.
As a MIDI controller, this thing is awesome!! Just about any of the buttons, sliders, knobs (except for the pitch-bender), and pads can be assigned to broadcast any MIDI messages you want, whether it be for selecting instrument or effect programs, controlling mixing or effects in your software, controlling other MIDI compatible devices, or for playing instruments. In my case, I am driving reverb and echo parameters within my ancient Alesis Quadraverb with sliders on the MPK88 and I can honestly say that, after owning my Quadraverb for 18 years, I haven't gotten nearly the value out of it that I have in the last few weeks under MPK88 control. And, any MIDI controls you program can be saved in a multitude of presents, so you're up and running with a twist of a knob and the press of a button. The only two things I'd like to see added are a user-definable keyboard velocity curve added to the resident five (LINEAR, LOG1, LOG2, EXP1 and EXP2) curves and I would like to be able to tune the threshold velocity that causes a MIDI velocity value larger than "1" to be sent when a key is pressed (for us newbies to hammer-action that sometimes don't reach the default threshold velocity for an instrument to make a sound).
One little nit-picky complaint I have is that to get the MPK88 to broadcast internally generated MIDI messages to its own MIDI-Out port, you must also have a 6 Volt, 1Amp external power supply (Akai recommends the Akai MP6-1 which is, unfortunately, not a regularly stocked item at most pro-audio stores) plugged in because, if the MPK88 is running on USB power, it reserves the on-board MIDI-Out port to echo messages coming from your computer. This is not a big deal because you can just have your computer echo the MPK88's USB messages back to the MPK88, but I think the behavior of the MPK88's MIDI-Out port should be user configurable.
In summary, I'm extremely pleased with the Akai MPK88.
* 88 fully weighted, hammer-action keys
* A huge assortment of fully programmable knobs, sliders, and pads
* Would be happier with less "plasticky" keys and aluminum shell
* On-board MIDI-Out port behavior is not user configurable