Eternal Daughter is an epic platform game that took myself and my friend Jon two years to make and nearly destroyed our immortal souls. It's an homage to some of our favorite games from our preteen years, like Super Metroid and Castlevania: SOTN.
It is pretty hard, but extremely fun, plus it is free. It was made in 2002 and the only downside to it is that you can't play it in true fullscreen view. It just does a set ratio and puts a huge black frame around it to cover your screen.
Some of you may have already heard about it or played it, but if you haven't, here is a http://www.derekyu.com/games.html to where you can download it, along with more of Derek Yu's games.