Great games without a Sequel/Prequel/Spin-Off???

Anachronox. Get it at GOG.com.

To the Moon.

Fahrenheit/Indigo Prophecy.

-The World Ends With You
-Muramasa: The Demon Blade
-Beyond Good & Evil
-Sleeping Dogs
-Cave Story
-Retro City Rampage
-Mark of the Ninja
-L.A.Noire
-Dust: An Elysian Tail

Surprising hard question, I had to take a close look into my game library.
From 2013: Monster loves you!
From 2012: Botanicula, Costume Quest, Quantum Conundrum (didn't played it yet), Snapshot and To the Moon.

XIII (a sequel was planned but never done), Alan Wake (American Nightmare is not a sequel), Dishonored, Hotline Miami, LA Noire, Mark of the Ninja,

Wasn't Shadow of the Collosus a sequel to Ico technically?

Bulletstorm

ive heard nice things about rogue galaxy

Legend of Dragoon. Cries self to sleep

Wait, what? Shadow of The Colossus is a 3 part story. >_>

I would recommend FTL although I haven't bought the game. I have watched the gameplays online and the story is so great you need to try it

Call of Duty (post-2008). They only have one they just re-release it every year with different graphics and slightly more annoying multiplayer users.

Bastion , fortixD:

Dark Messiah of M&M
If you want to know the complete lore, you should play HoMM5 (which is TBS), but Dark Messiah its only about a character and you dont realy need to know about all the conflicts to understand the story..

E.T. the Extra-Terrestrial

Lots of free copies out there, you just need a shovel!