I still have my trusty FZ-1 that I've owned for over 16 years now. I use it all the time. It's definitely old in features but it goes great. It samples at 36k rather than 44k, so the quality isn't quite CD (but still completely useable and fine for me!) but I wouldn't call it a lo-fi sampler. Can hold up to 64 samples in 8 banks of sounds. Each bank can have up to 64 splits of samples - so you can have a single sample on each key, or less if you like. Or you can play each of the 64 samples singly, stretched across the whole keyboard. You can also have 64 sample velocity layers on each key, which is great for making realistic drum kits. Good MIDI implementation. sends/receives Velocity + aftertouch, Prog change etc. Digital filters that are over-the-top wicked hehe!! 8-step ADSR for envelope and also for filter. 8-step looping (!!!!). Only 8-note polyphony, but you can work around that unless you want to play classical piano on it. Single mix output plus 8 separate monophonic out jacks you can assign samples to.
I think its easy to use - menu driven. Sample editing on screen visually. I didn't touch the manual for a whole week when I first got it, and then that for was something more complex like crossfading a sample etc.
Synthesis section is lots of fun - the additive sine synthesis is fun to do random sounds with. I once came up with this incredible Hammond B3 sound accidentally and forgot to save it - d'oh!!
Simple standard preset wave section - square, triangle, sine, a few others
Hand drawing is ok but a bit tedious - you use the <> cursors and entry slider to draw, which feels a bit clumsy. Still fun though.
I'm not a keyboard player by trade, so I wouldn't know a good keyboard feel, but it feels smooth, fairly long travel. I use it as my master keyboard for all my synth modules. Feels natural enough. It's a very quiet keyboard, which is good sequencing at 2am in the morning - it doesn't make much mechanical noise (The DX7 my friend used to have would wake the whole house up - click click click click).
The OS is built into ROM, so you don't have to start up with a boot disk before you can use it, like some of the other samplers of its era. Just switch on and start sampling. Saves samples to floppy disk. The factory sample library (140 sample disks) is also available for free on the net to download and sample dump into the FZ (I have a copy if you can't find it via Google).
Sample format is proprietry Casio but you can do sample dump via MIDI port to computer. Once on your computer you can convert the sample to a WAV file, or from a WAV file to Casio format and upload it to the Casio via sample dump with a small freeware program called "Casio FZ File Transfer Utility ": http://hem3.passagen.se/highpuls/index.htm
Its under the HW & SW drop-down menu.
You can use a program called FZ-Dump for dumping via the parallel port on the FZ which is much quicker than MIDI dump, but you have to have a special cable to do it - its not a normal parallel port cable in the wiring. You can DIY a cable here: http://www.geocities.com/sirmidi/fzsample.html
and here for the program (with included wiring map): http://www.synthzone.com/midi/casio/fz1/
Also, a good collection of resources, including a free MIDI sample dump software and editor here: http://hem3.passagen.se/highpuls/index.htm
Yahoo Groups FZ forum: http://launch.groups.yahoo.com/group/casiofz1/
Butchy's FZ site with DIY mods and repair info.
Like all older samplers with floppy drives, the drives eventually wear out. In the FZ, when you put a disk in the drive and load a sample, the sample loads, but when it finishes loading and the drive light goes out, the drive will still spin while not in use, and gradually wear itself and the disk out. Make sure you eject the disk as soon as its loaded and you'll save it lots of wear and tear. Consequently, any FZ you buy may have a dead drive - check it out first before buying. It is not a normal PC floppy drive in its connections, but you can use a normal one if you modify the floppy cable - info about that on the Butchy site. The Butchy site has details on how to DIY: http://www.buchty.net/casio/fz1-diskdrive.html
The main problem with the FZ (and also the VZ synths) is the cursed LCD dying backlight. They all wear out over a period of a few years. When they are completely dead they begin to interfere with the power supply and cause the machine to glitch at first and corrupt samples, then finally start randomly crashing the machine, and finally totally lock up the machine with a high pitched whistle coming from the screen. The easy solution is to replace the backlight: http://www.midi-rakete.de/eng/elfolie.htm
Instructions on replacing it here: http://www.geocities.com/sirmidi/fzdisplay.html
It will still wear out again though. The permanent solution is to pull the backlight out and replace it with an LED backlight - it will last forever then.
Hope that helps. You can pick an FZ up cheap these days, maybe less than $100. The keyboard version is all metal and HEAVY. There is a rack mount version called the FZ-10M, and a later, expanded model called the FZ-20M which also has a SCSI port for dumping samples to a SCSI hard drive. The FZ-1 comes with 1MB of sample ram standard, with a 1MB expansion board available for a total of 2MB. Make sure you pick up one with the expansion, it's much better with the extra memory, and the expansion boards are rare. The FZ10M and FZ20M come standard with 2MB. There is a mod on one of the sites I mentioned to expand it to 4MB!!