I thought Red Faction was popular and sold well? It had a relatively high-profile sequel and everything (even though said sequel pretty much killed it). Edit: Wasn't a sequel supposed to come out soon?
You know, one series that doesn't get much love is Armored Core. The learning curve and anime robots are pretty big barriers, but I thought the gameplay was pretty sophisticated; there aren't many games with a deep planning phase anymore, and almost none that do it quite like this series.
If I had to pick from the list, though, it would be STALKER.