What type of keyboard (synth, piano ...)? How many octaves?
What controllers (pitch, modulation, sustain ...)?
What connection (Audio, MIDI pedals ...)?
How many sounds, effects? What styles? Are they edited?
Via a utility Mac / PC?
What polyphony? ...

UTILIZATION

The general configuration is simple?
Editing sounds and effects is easy?
The manual is clear and sufficient? ...

SOUNDS

The sounds they are suitable to your style of music?
Are they realistic?
The effects are they effective and appropriate?
The expression is good? (Response to velocity, aftertouch)?
What are the sounds you prefer, you hate? ...

OVERALL OPINION

For how long have you been using it?
What thing do you like most/least about it?
Did you try many other models before getting this one?
What is your opinion about the value for the price?
Knowing what you know now, would you make the same choice? ...