Cortex command- Obvious reasons.
Magicka- Because magicka.
Terraria- Basicly minecraft with guns, bombs and a unique variety of different bosses.
The binding of Isaac- Random level layout every time you play and a variety of different items to spice up the gameplay makes for an interesting and unique game.
Facade- So bad it's funny.
Intrusion 2- Bosses. Not like other games where it's all "shoot him in the head a number of times with a large machine gun". In Intrusion 2 you either learn the boss's patterns or get ground into the dirt.

Thank you for reminding me of this thread.
And yes, I'd love the add Magicka to my list, for it's the greatest mage suicide coop simulator ever.
Excuse my horrible English there. Was sleepy in the morning.

Welcome. Magicka is quite a fun game, although I'm stuck on that level with the ski free reference at the beginning.