Contra ReBirth
I was never big on Contra - it's too hard for me. In the company of friends, though, the quest to get to the next checkpoint without a Game Over can be quite fun.
That's where the genius bit of ReBirth comes in: it can be finished in an afternoon, with plenty of time to spare.
The game charms with its 16-bit visuals and music (with minimal use of modern graphical sophistication), and there's a campy, ridiculous story to boot. For a $10 bite-sized portion of Contra, this is pretty perfect. Just don't expect anything more.
Progress: Finished on Normal (co-op)