In some classes we tried to make a brief list of what makes a game great. I have my own ideas (which I briefly discussed in my contribution to Hobby Games: the 100 Best), and I intend to write a separate article about that, so I'll just list what we came up with in class in no particular order.
Innovation--it's good to be first
Improving realism (e.g. destructible environments Red Faction) (bullet time) (scars) (camera movement) etc.
Really good gameplay (playability)
PvP, team play--something other than person vs. computer
Variety of modes of play (online, pvp, MMO)
Verisimilitude of the environment--when you’re there, it feels like you’re really there
Your character can grow and change (skills, attributes)
Good interface and tight game controls
"The worst form of inequality is to try to make unequal things equal." -- Aristotle
"Always do right--this will gratify some and astonish the rest."Mark Twain
"A designer knows he has achieved perfection not when there is nothing left to add, but when there is nothing left to take away." Antoine de Saint-Exup'ery
"Not everything that can be counted counts, and not everything that counts can be counted." Albert Einstein
"Make everything as simple as possible, but not simpler." Albert Einstein