Thou shalt have autosave
Thou shalt not have specific save locations
Thou shalt not make they game impossible to finish if one mistake is made (Oblivion!!!!)
Thou shalt not have infinately spawning enemies
Thou shalt not make a God of War, Devil May Cry or Final Fantasy clone
Thou shalt make thine enemies in Final Fantasy style combat not have 9 turns after the other
Thou shalt not make more than 2 sequels
Thou shalt not make portal references
Thou shalt not have pointless cutscenes and quicktime events
Thou shalt have decent voice actors.