There is a Steam sale on WB games right now. I picked up Middle Earth: Shadow of Mordor. The Batman games are also on sale, but I don't like those
The best game ever is Half Life 2, so be sure to buy it along with the episodes.
The Witcher games are honestly some of the best when it comes to story and whatnot, and you can usually find the first two on sale for under 5 dollars, so I would say to shoot for those. Aside from that if you're not into RPG's, then I would definitely say that the bioshock series is great, and personally I think that infinite is the best in terms of storyline, especially with the burial at sea dlc.