Imho, before anything else, a decent looper needs to have FEEDBACK (or DECAY or whatever you want to call it), controlable either via Exp.Pedal or by two preset levels between which you can toggle (like: 100% – 70%). Without the possibility to let looped material (slowly) decay while you either just play or overdub new material, a looping device is pretty useless and un-musical to me.
+1 for MULTIPLY as written above.
UNDO – yes, but MORE than last overdub…all the way back to the first loop
Looptime should be at least 1 minute (please,…the EDP had 200sec mono @ 16/44.1 with only 16mb of RAM!)
Real time pitch shift and time stretch
at least 2 parallel stereo tracks (with the option to work independently or synced
for now… 😉