Hotline Miami is such a good game. The gameplay is so fast paced and brutal. I am so excited for the sequel.
A game I have been really getting into lately is Gratuitous Space Battles (spelling?). It's a game where you control fleet of space ships to go to battle with other space ships. You can build ships, as well as choose what ships you have in your fleet, and there are multiple different races you can play as. I am absolutely terrible at it, but I still have so much fun playing it.
A lot of people in the thread mentioned Cave Story. I am on my third play through of it, so many different ways to play it, and there are a lot of weapons you can use, so you have to do multiple runs to do everything.