For me I look for something thats new and innovative. We all, of course, love a game that is fun and can be played for a long time without getting sick of it. Sadly, though, this is very much something that can only be found out once you buy the game and give it a whirl yourself.
Recently, I have felt as if the gaming companies are really struggling to come up with new bright product ideas. For example, this game could have really been epic!!! This may just be me, but I get the feeling that many elements have been taken from other games of the same genre dotted about (its clear as day to me), this translates to me as laziness and an overkeeness to release a title as quickly as possible. If you focus on the FPS market say ~ 80% of recent releases have all been much of the same recycled ideas and gaming elements.
So yeah moral of the story, dont listen a jot to the hype/promo before the release of a game. If the demos look interested then give it a try. If you buy a dud then put it down to experience and trade it in, but if you find a nugget then high five and enjoy!!