An amazing freeware gem if I've ever seen one; GoP puts you in the role of Tela, a boy whose sister has fallen ill with an incurable disease. Legend tells of healing waters in paradise which can heal any illness, thus Tela sets off to get these waters and save his sister.
Guardian of Paradise has a very zelda-ish feel to it which actually ends up being a good thing. It is very easy to jump right into and has a surprising amount of length to it. You have your basic attack, the sword, as well as magic abilities that you will get from elemental spirits along the way.
This game deserves at least an afternoon of your time, if not more.