Best single player game? Metal Gear Solid, done, sold. That series is AMAZING! Once you start with Metal Gear Solid, you're going to want to play the second, then the third, then the epic and amazing conclusion of the 4th and once it's all said and done, after experiencing a vast amount of different emotions while playing, you'll lean back in your chair and the only word you'll be able to even think about is "Wow...."
The Metal Gear series is my favorite series and I'd recommend it to anyone! Seriously the single player experience is......ridiculous. The plot, characters, and everything that went into each game is baffling.
But other than that, I'd recommend Heavy Rain, God of War, Assassins Creed, or Dynasty Warriors 7 <----the better DW game that tells the historical story more brilliantly especially if you're into history related games like Assassins Creed then you will like Dynasty Warriors. I could go on but I think these titles/series stand out for themselves =)