"Must own" games?

The only must own game this Fall in my book is Modern Warfare 2.  Everything else can wait til next year or is a rental from Gamefly. (Brutal Legend, Borderlands, Way of the Samurai 3 [Hell yeah!], L4D2, Assassins Creed 2,  and Army of Two T40D.  I would be buying Ballad of Gay Tony but seeing as I can rent Episodes from Liberty City, I'll just be going that route.  
Seriously people, buying merely two of these games will set you back enough money to support a half year of Gamefly getting two games at a time. Aside from Borderlands and L4D2, every one of those games in my rental list will be collecting dust on gamer's shelves or traded in before before the New Year. I just don't understand why people buy single player experiences that don't last more than thirty hours.