This mint Electro 2 was used in our studio on a couple projects. It is an incredible keyboard with spot on Rhodes, Wurlitzer Clavinet and B3 sounds.
The newer Electro 3 and 4 claim to have more realistic samples and we tried them but found them to be less realistic. The newer samples were sampled with ambiance or cabinet effects rather than a simple close miked or direct sound. To our ears, this sounded less realistic and more, well sampled. The effects of the later models just didn't match the effects of the Electro 2. That was our take anyway.
After comparing them side by side we opted to stick with the Electro 2. Its easy to get a good direct sound (with no modeled mic/cabinet trickery) and then add solid effects such as spot on Leslie w/ foot control, vibrato, stereo tremolo, phaser, tube saturation, auto wah. The sounds sit where we expected in a recording.
The keyboard is absolutely the best we have played on any keyboard. The Fatar waterfall keyboard it great for electric piano and B3. You can do all the B3 key tricks. It has a quick spring back but is not so springy that Electric piano feels unnatural. Here's the thing though. There is something about the velocity map that we have not found in any other keyboard. We used compared it with several high end controllers both playing the same vst instruments and the Nord keyboard brought the samples to life while the others keyboards seemed flat or over exaggerated regardless of which velocity mapping we tried. The only thing that came close was a fatar weighted piano controller but that just didn't work well for B3 or synth or anything but electric pianos really. The waterfall keyboard is the best overall choice in our opinion for that "if you only had one keyboard" scenario.