Controlls , ease of use , ie easy to get into..
well covered in learning process and most of all graphics that is not too little nor too much...
good example is...zool 1 ECS ...is awesome , zool 1 AGA suxx....
Xtr 1 had lousy controlls for beginners..., xtr upd (1.2) has sweet controlls....
anyway.... music also makes a game more playable...if its good anyway
cheers