The six signals of quality in software
Reliability
Does the software technically perform as expected, all of the time? This means no bugs, no downtime, no errors, and so on.
Speed
Does the software react to input instantly, or as near as practically possible? For those tasks that must take longer, are they as fast as possible?
Clarity
Does the person using the software understand everything?
Efficacy
Can the person do what they need to do with the software?
Efficiency
Can the person do what they need to do with the software as easily as possible?
Beauty
Is the software as aesthetically pleasing as possible?