I've been using this keyboard for four years now after receiveing it as a Christmas gift. At the time (1997) it was the only Sequencer/Synth keyboard available for under $300 and was a tremendous value then, and now. The display is well thought out and set up (although I could do with out the keyboard keys and grand staff that show you what notes you're playing). It amazingly easy to use. In fact, I learned how to use it from the manual without even turning the thing on because when I opened it up on X-Mas morning the power supply was bunk.
As far as its synth abilities, it is a 4 DCO (2-4 DCO's if you use the layer function, 1-2 without) wavetable synth with 24 voice polyphony which, supirisingly, is quite adequate. I've only had voice stealing once and that was from a 16 channel rendition of Beethovens 5th. My only gripes are the lack of programmability in the Amp.Envelope and PitchEnvelope (or Amp.Set and PitchSet). The only parameters that are user defineable in those areas are the attack and release rates and the pitch and tuning. It's not a big problem though due to the great preset envelopes they give you to work with.
The sounds are all good, nice clean (headphone, arghh, sorry no dedicated Line-Out) output, genreal midi, fair SysEx implementation (can edit most parameters through SysEx), sequencer works best as scratch pad. Not enough memory for me (two songs with a total of 5,200 notes divided up between the two). I can make due with the 6 channels that are available to record on. No quantization, does have a pretty efficient and east to use step-sequencing function (I was sequencing within the first hour of using it). Good overall board for the beginner looking to learn basic to intermediate sequencing, MIDI, and synth programming info. I would buy one again, especially at the prices they go for ($80-$130). Some more gripes, every keyboard has some kind of problem. The effects, if one can call them that, are rather poor given the other features of this keyboard. There is only one type of effect (a reverb) and only four settings (Hall, Stage, Room, and Off). It responds to external transpose messages as pitchbend messages (even in it's "General MIDI" mode). You don't hear a gliss down to the note, it's like setting the pitch bend wheel to a value of one octave, holding it down or up and playing. The sounds to sound right. It plays the internal transpose command correctly. Another problem for some (not me though, I bulk dump into my computer) might be the fact that there is no backup battery. This meaning, of course, that if the keyboard goes more than 15 seconds without its wall wart or the six C-cell batteries needed to power it, you lose all of your synth presets and all of the sequencer info. Let's see, other strong points include the sturdy build (even though it's plastic), the great sounds, the ease of use. This keyboard is great for taking on road trips where You might want to do a little playing/song writing, or at the park, on a bus, in a boat, it's great for hauling onto your bed and laying down to do some sequencing right before you go to sleep (at least that's what I do).
Overall a great buy for the beginner looking for a sequencer/synth/great GM soundset or for anyone looking for those actually. If you're thinking about buying this keyboard, check out the Casio WK-1300, it's the same internal components but with a better speaker system, backlit display, and a real pitchben wheel (the CTK-601 has Pitch Bend Up and a Pitch Bend Down buttons). It's a shame that this keyboard didn't catch on, it would've meant some serious competition in the under $700, under $500, and under $300 market (resulting in better keyboards at better prices for all, SCORE!) IF YOU ONLY READ ONE PARAGRAPH IN THIS REVIEW, READ THIS ONE BELOW THE ASTERISKS (*) ************************************************* Before I end this, I'm working on two things for this keyboard; (1)Amp.Set and PitchSet charts showing what each preset does (there's no index in the manual) and (2)An Editor/Librarian for Windows (there's one out there for DOS, but it's really poor and I could never get it to work right). If You have any questions, would like to contribute to my projects, or want a copy of the Editer/Librarian when it's done, please don't hesitate to email me.