Dead Space had a quite decent length, it took me 12 hours to finish. If you're a fan of cheesy sci-fi horror with quite a fun arsenal of weaponry then definitely check it out.
inFamous. It'll take around 20 or so hours. I highly recommend this one. Super-hero sandbox at its absolute best.
Mass Effect series, TPS/RPG hybrids. take 8-12 hours if you're only doing the main-quests, much longer with side-quests. Although, the difference between the two games is that ME1 has more emphasis on RPG elements while ME2 leans more on the shooting elements. But the first game has much superior plot and writing.
Red Dead Redemption. It's a Rockstar sandbox game so you'll definitely get your money's worth. Be warned that the game's pacing suffer especially around the middle part of the game but it's worth checking out.
RE4. Ok, this is an old one. I actually played it quite recently and was shocked to know that it took me 19 hours to finish, It's also one of the best TPS I've ever played. you can find it quite cheap nowadays.
