Feature:
The CTK2000 is a basic keyboard with no frills. The CTK3000 is step up from 2000 with more sounds and pitch-bend. The CTK4000 features 48 note polyphony, even more sounds, an arpeggiator, but no pitch-bend. The CTK5000 predictably is a step up from the CTK4000 with a pitch=bend included. A missing adaptor is a gotcha but easily remedied buy purchasing any 9VDC 1Amp adaptor from the market. For some reason, the portamento effect seems to have fallen out of favor and the Casio keyboards no longer feature it. The preset-bank feature is useful to store keyboard setup combination but is marred by the fact that the keyboard does not feature non-volatile memory. I love the arpeggiator feature and music styles feature of the keyboard. The arpeggiator features quite a few combinations - octave up/down/both/random,note lengths etc. The preset styles are neat. Choose a rhythm style. Keep the style button pressed for 2 seconds - the recommended instrument and style tempo are set automatically. The music style feature lets you automatically select the style and tone too. Choose #61 (careless whispers) and the rhythm and tone are set automatically to 16-beat1 and Sax. The keyboard features USB connection but no MIDI in/out/pass-through. Typical Casio; won't give you best of both the worlds. The sampling feature is of not much use since it doesn't come with a sample editor. If you sample a tone or style, there is no way for you to customize the start-stop of the sample or any other manipulation. The keyboard features touch-sensitivity (2 levels) but lacks after-touch (not expected at this price point too). Due to lack of the hammer-action, don't expect to play a sequence of 32nd notes on this keyboard, even 16th notes will be tough. 8th notes though can be accomplished easily by first-timers. Loads of interesting functions like transpose, arpeggiator-hold, reverb/chorus levels are hidden away behind a small button titled functions. A sustain controller can be attached but not a breath controller.

Quality:
Very plasticky and featuring a passe silver finish, I was tempted to buy the CTK300 or the CTK5000 (black). But what made me buy the CTK4000 was the fact that feature-wise, this is a superior product when compared to the CTK3000 and the CTK5000 was priced beyond the budget restriction I had set for myself. The keyboard is surprisingly light though and will definitely save my back as I go carting around town to friend's or trainer's place. The keyboard keys are nice and long but not springy enough for virtuoso pianist. Then again, no virtuoso will be caught dead using a Casio learner's keyboard. So the point is moot.

Value:
Compared to Yamaha (the other manufacturer of home keyboards), this keyboard is definitely a better deal because of the higher number of tones, polyphony, and customization features. The nearest Yamaha still has fewer features than this and costs 40% more.

Desirability:
Sex appeal - Zero. But should you get it? YES. The keyboard is power-packed for entertainment and in the end that's what matters.

Sound:
The CTK-4000 comes pre-loaded with 570 tones. Since the keyboard is GM compatible, the base tones are 127 and the rest of the tones are variations of the 128 tones. While some of the tones are very similar to each other (with only minor variations in chorus/phase), others are dramatically different. The product also comes with 180 styles to play along. Users can sample their own tones and styles and store on the keyboard (memory requires batteries). The tones and styles are very sweet sounding and melodic. They also seemed to be multi-sampled across the keyboard and at different pressure levels. Pressing the keys faster distincly produces a clangy piano sound, not just a louder piano sound. The styles can be manipulated to individually switch off parts. For ex: users can switch off the chords/harmony parts of style and only opt for drums and bass.

Ease of Use:
The keyboard is quite easy to use. Buttons are neatly labeled. Accessing basic functions is a no-brainer. Advanced functions require reading the manual and a few experiments on the keyboard. The 2-second press for presets functions makes it very easy to quickly setup the keyboard for optimal playback. Since this keyboard is squarely targeted for the family home rather than the stage, this feature is much appreciated. Most functions are selected through a number pad. A jog-wheel to select parameters would have been nice.

Support:
The keyboard came with 3 years warranty, so be sure to get it stamped by the dealer and preserve the bills of purchase. Roll them and put them in the battery compartment if you are the type that loses papers. I used to own a Casio PT-20, a SA-20, a MA-120 and never had to revert to the manufacturer. So here's keeping my fingers crossed that Casio quality control is still the same as it used to be. The manual mentions downloadable software on Casio's site. The s/w can be used to save the keyboard settings, user tones and styles and quickly load them back on the keyboard. I however could not find any reference to software on Casio's site.

Overall:
While this is a keeper, I may want to acquire a small MIDI controller purely for functions such as pitch-bend or a few control knobs.