all games are not created equal

Mass Effect has a wonderfully enthralling story that makes you want to continue playing despite the weak combat system.  Fable 2 has nearly no story at all and derives all of its entertainment from capabilities outside of the main story line.

Both games have significant weaknesses in my opinion.  However it is fable 2 that really fails in my mind to live up to expectation.

Fable 2 allows for the exploration of a world and gives you the ability to become whoever you want to be.  Kill innocents, bad points.  Kill bandits, good points.  The problem is this formula is too simple.  There are no complex decisions in Fable 2 whatsoever.  Instead the game stays shallow.  This is not to say that it isn't fun.  Fable 2 is very entertaining for the first 8-10 hours, but after that you realize the simplicity and stop playing there.

Mass Effect on the other hand has a very deep story that keeps you guessing.  The management of your characters status (good/evil) relies on making complex decisions and, in some case, forces you to make a decision in which you don't know if the outcome is for good or evil.  However, the combat system is so weak that it makes fighting nearly no fun at all.  If you are all about action and don't care much about the story, ME will bore you instantly.

All that being said, ME has replayability that F2 just doesn't.  Both games needed 8-12 months more in development.  But in the end, it is F2 really disappoints.