While auto-attack is great, sometimes it doesn't proc properly, other times your out of distance and don't realize it (sometimes due to the terrain?) etc.
So why not just add in a little bar that goes from empty to full? When its full you know auto-attack is ready to use.
This might also bring in some strategy about when to use abilities and such adding to the tactical part of the battle system.
And of course you'd be able to turn it off.